你想通过进度条来反映什么？ 而不是下载文件（因为它很大）或处理文件？ 
 
 反映处理文件的进度条 
 
 你的进度条不会改变，因为你的方法是同步的 - 没有别的事情会发生。 BackgroundWorker类完全适用于这类问题。 它以异步方式完成主要工作，并能够报告进度已更改。 以下是如何更改巡视方法以使用它： 
 
private void button1_Click(object sender, EventArgs e)
{
    string text =  textBox1.Text;
    string url = "http://api.bing.net/xml.aspx?AppId=XXX&Query=" + text + "&Sources=Translation&Version=2.2&Market=en-us&Translation.SourceLanguage=en&Translation.TargetLanguage=De";

    XmlDocument xml = new XmlDocument();
    xml.Load(url);
    XmlNodeList node = xml.GetElementsByTagName("tra:TranslatedTerm");

    BackgroundWorker worker = new BackgroundWorker();

    // tell the background worker it can report progress
    worker.WorkerReportsProgress = true;

    // add our event handlers
    worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(this.RunWorkerCompleted);
    worker.ProgressChanged += new ProgressChangedEventHandler(this.ProgressChanged);
    worker.DoWork += new DoWorkEventHandler(this.DoWork);

    // start the worker thread
    worker.RunWorkerAsync(node);
}
 
 现在，主要部分： 
 
private void DoWork(object sender, DoWorkEventArgs e)
{
   // get a reference to the worker that started this request
   BackgroundWorker workerSender = sender as BackgroundWorker;

   // get a node list from agrument passed to RunWorkerAsync
   XmlNodeList node = e.Argument as XmlNodeList;

   for (int i = 0; x < node.Count; i++)
   {
       textBox2.Text = node[i].InnerText;
       workerSender.ReportProgress(node.Count / i);
   }
}

private void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // do something after work is completed     
}

public void ProgressChanged( object sender, ProgressChangedEventArgs e )
{
    progressBar.Value = e.ProgressPercentage;
}
 
 反映下载文件的进度条 
 
 尝试使用HttpWebRequest获取文件作为流。 
 
// Create a 'WebRequest' object with the specified url. 
WebRequest myWebRequest = WebRequest.Create(url); 

// Send the 'WebRequest' and wait for response.
WebResponse myWebResponse = myWebRequest.GetResponse(); 

// Obtain a 'Stream' object associated with the response object.
Stream myStream = myWebResponse.GetResponseStream();

long myStreamLenght = myWebResponse.ContentLength;
 
 所以现在你知道这个XML文件的长度。 然后你必须异步读取流中的内容（ BackgroundWorker和StreamReader是一个好主意）。 使用myStream.Position和myStreamLenght来计算进度。 
 
 我知道我不是很具体，但我只是想让你走向正确的方向。 我认为在这里写下所有这些东西是没有意义的。 在这里你有链接，可以帮助你处理Stream和BackgroundWorker ： 


What exacly do you want to reflect by progress bar? Rather downloading the file (because it's big) or processing the file?
 
Progress bar reflecting processing file
 
Your progress bar doesn't change because your method is synchronous - nothing else will happen unit it ends. BackgroundWorker class is designed perfectly for this kind of problems. It does main work in an asynchronous manner and is able to report that progress has changed. Here is how to change tour method to use it:
 
private void button1_Click(object sender, EventArgs e)
{
    string text =  textBox1.Text;
    string url = "http://api.bing.net/xml.aspx?AppId=XXX&Query=" + text + "&Sources=Translation&Version=2.2&Market=en-us&Translation.SourceLanguage=en&Translation.TargetLanguage=De";

    XmlDocument xml = new XmlDocument();
    xml.Load(url);
    XmlNodeList node = xml.GetElementsByTagName("tra:TranslatedTerm");

    BackgroundWorker worker = new BackgroundWorker();

    // tell the background worker it can report progress
    worker.WorkerReportsProgress = true;

    // add our event handlers
    worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(this.RunWorkerCompleted);
    worker.ProgressChanged += new ProgressChangedEventHandler(this.ProgressChanged);
    worker.DoWork += new DoWorkEventHandler(this.DoWork);

    // start the worker thread
    worker.RunWorkerAsync(node);
}
 
Now, the main part:
 
private void DoWork(object sender, DoWorkEventArgs e)
{
   // get a reference to the worker that started this request
   BackgroundWorker workerSender = sender as BackgroundWorker;

   // get a node list from agrument passed to RunWorkerAsync
   XmlNodeList node = e.Argument as XmlNodeList;

   for (int i = 0; x < node.Count; i++)
   {
       textBox2.Text = node[i].InnerText;
       workerSender.ReportProgress(node.Count / i);
   }
}

private void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // do something after work is completed     
}

public void ProgressChanged( object sender, ProgressChangedEventArgs e )
{
    progressBar.Value = e.ProgressPercentage;
}
 
Progress bar reflecting downloading file
 
Try using HttpWebRequest to get the file as a stream.
 
// Create a 'WebRequest' object with the specified url. 
WebRequest myWebRequest = WebRequest.Create(url); 

// Send the 'WebRequest' and wait for response.
WebResponse myWebResponse = myWebRequest.GetResponse(); 

// Obtain a 'Stream' object associated with the response object.
Stream myStream = myWebResponse.GetResponseStream();

long myStreamLenght = myWebResponse.ContentLength;
 
So now you know the length of this XML file. Then you have to asynchronously read the content from stream (BackgroundWorker and StreamReader is a good idea). Use myStream.Position and myStreamLenght to calculate the progress.
 
I know that I'm not very specific but I just wanted to put you in the right direction. I think it doesn't make sense to write about all those things here. Here you have links that will help you dealing with Stream and BackgroundWorker: