方法一：

/**
 * 发送post请求
 * @param string $url 请求地址
 * @param array $post_data post键值对数据
 * @return string
 */
function send_post($url, $post_data) {

  $postdata = http_build_query($post_data);
  $options = array(
    'http' => array(
      'method' => 'POST',
      'header' => 'Content-type:application/x-www-form-urlencoded',
      'content' => $postdata,
      'timeout' => 15 * 60 // 超时时间（单位:s）
    )
  );
  $context = stream_context_create($options);
  $result = file_get_contents($url, false, $context);

  return $result;
}

//使用方法
$post_data = array(
  'username' => 'stclair2201',
  'password' => 'handan'
);
send_post('//www.jb51.net', $post_data);

方法二：Socket版本

<?php
/**
 * Socket版本
 * 使用方法：
 * $post_string = "app=socket&version=beta";
 * request_by_socket('chajia8.com', '/restServer.php', $post_string);
 */
function request_by_socket($remote_server,$remote_path,$post_string,$port = 80,$timeout = 30) {
  $socket = fsockopen($remote_server, $port, $errno, $errstr, $timeout);
  if (!$socket) die("$errstr($errno)");
  fwrite($socket, "POST $remote_path HTTP/1.0");
  fwrite($socket, "User-Agent: Socket Example");
  fwrite($socket, "HOST: $remote_server");
  fwrite($socket, "Content-type: application/x-www-form-urlencoded");
  fwrite($socket, "Content-length: " . （strlen($post_string) + 8） . "");
  fwrite($socket, "Accept:*/*");
  fwrite($socket, "");
  fwrite($socket, "mypost=$post_string");
  fwrite($socket, "");
  $header = "";
  while ($str = trim(fgets($socket, 4096))) {
    $header .= $str;
  }

  $data = "";
  while (!feof($socket)) {
    $data .= fgets($socket, 4096);
  }

  return $data;
}
?>

方法三：Curl版本

<?php
/**
 * Curl版本
 * 使用方法：
 * $post_string = "app=request&version=beta";
 * request_by_curl('//www.jb51.net/restServer.php', $post_string);
 */
function request_by_curl($remote_server, $post_string) {
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $remote_server);
  curl_setopt($ch, CURLOPT_POSTFIELDS, 'mypost=' . $post_string);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($ch, CURLOPT_USERAGENT, "jb51.net's CURL Example beta");
  $data = curl_exec($ch);
  curl_close($ch);

  return $data;
}
?>

下面是其他网友的方法：

class Request{
  public static function post($url, $post_data = '', $timeout = 5){//curl
    $ch = curl_init();
    curl_setopt ($ch, CURLOPT_URL, $url);
    curl_setopt ($ch, CURLOPT_POST, 1);
    if($post_data != ''){
      curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);
    }
    curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1); 
    curl_setopt ($ch, CURLOPT_CONNECTTIMEOUT, $timeout);
    curl_setopt($ch, CURLOPT_HEADER, false);
    $file_contents = curl_exec($ch);
    curl_close($ch);
    return $file_contents;
  }
  public static function post2($url, $data){//file_get_content
    
    $postdata = http_build_query(
      $data
    );
    
    $opts = array('http' =>
           array(
             'method' => 'POST',
             'header' => 'Content-type: application/x-www-form-urlencoded',
             'content' => $postdata
           )
    );
    
    $context = stream_context_create($opts);
    $result = file_get_contents($url, false, $context);
    return $result;
  }
  public static function post3($host,$path,$query,$others=''){//fsocket
    $post="POST $path HTTP/1.1\r\nHost: $host\r\n";
    $post.="Content-type: application/x-www-form-";
    $post.="urlencoded\r\n${others}";
    $post.="User-Agent: Mozilla 4.0\r\nContent-length: ";
    $post.=strlen($query)."\r\nConnection: close\r\n\r\n$query";
    $h=fsockopen($host,80);
    fwrite($h,$post);
    for($a=0,$r='';!$a;){
        $b=fread($h,8192);
        $r.=$b;
        $a=(($b=='')?1:0);
      }
    fclose($h);
    return $r;
  }
}