//1.发出请求
string url = "http://www.mzwu.com/test.apk";
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
request.AddRange(0, 1);
request.Timeout = 10000; //防止不支持时等太久
HttpWebResponse response;
try
{
    response = (HttpWebResponse)request.GetResponse();
}
catch (WebException ex)
{
    response = (HttpWebResponse)ex.Response;
}
//2.根据HTTP状态码判断是否支持断点续传
Console.WriteLine(response!=null && response.StatusCode == HttpStatusCode.PartialContent ? "YES" : "NO");