废话不多说，直接上代码

<?php
  // 暂不支持断点续传
  // $url = 'http://www.mytest.com/debian.iso'; 不知道为何获取本地文件大小为0
  $url = 'http://192.168.8.93/download/vm-672/18/0.vmdk';
  $file = basename($url);
  $header = get_headers($url, 1);
  $size = $header['Content-Length'];

  $fp = fopen($url, 'rb');
  if ($fp === false) exit('文件不存在或打开失败');

  header('Content-Description: File Transfer');
  header('Content-Type: application/octet-stream');
  header('Content-Disposition: attachment; filename="'.$file.'"');
  header('Content-Transfer-Encoding: binary');
  header('Expires: 0');
  header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
  header('Pragma: public');
  header('Content-Length: ' . $size);

  ob_clean();
  ob_end_flush();
  set_time_limit(0);
  
  $chunkSize = 1024 * 1024;
  while (!feof($fp)) {
    $buffer = fread($fp, $chunkSize);
    echo $buffer;
    ob_flush();
    flush();
  }
  fclose($fp);
  exit;