HttpClient httpClient = new HttpClient();
string result = httpClient.GetAsync("url?name=张三&age=18")　　　　　　　　　.Result.Content.ReadAsStringAsync().Result;
httpClient.Dispose();

HttpClient httpClient = new HttpClient();

HttpContent httpContent = new StringContent("{\"name\":\"张三\",\"age\":\"18\"}");

httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");

//HttpContent httpContent = new FormUrlEncodedContent(Dictionary集合对象);

//HttpContent httpContent = new MultipartFormDataContent();

string result = httpClient.PostAsync("url", httpContent)　　　　　　　　　.Result.Content.ReadAsStringAsync().Result;

httpClient.Dispose();

HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("url?name=张三&age=18");
request.Method = "get";

WebResponse response = request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
string result = reader.ReadToEnd();

response.Close();
reader.Dispose();

HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("url");
request.ContentType = "application/x-www-form-urlencoded";
request.Method = "post";

byte[] byteData = UTF8Encoding.UTF8.GetBytes("name=张三&age=18");
// Set the content length in the request headers
request.ContentLength = byteData.Length;

// Write data
using (Stream postStream = request.GetRequestStream())
{
    postStream.Write(byteData, , byteData.Length);
}

// Get response
WebResponse response = request.GetResponse();
// Get the response stream
StreamReader reader = new StreamReader(response.GetResponseStream());
string result = reader.ReadToEnd();

response.Close();
reader.Dispose();