<?php

  // $dumpFileName目录要有可写权限
  $DbHost = 'localhost';
　　$DbUser = 'root';
　　$DbPwd  = '123456';
　　$DbName = 'a';
  $fileName = $DbName . '_MySQL_data_backup_' . date('YmdHis) . '.sql';
　　$dumpFileName= "/var/$fileName";

　　header("Content-Disposition: attachment; filename=" . $fileName);
　　header("Content-type: application/octet-stream");
　　header("Pragma:no-cache"); 
　　header("Expires:0");
  
　　echo `mysqldump -h $DbHost -u$DbUser -p$DbPwd $DbName > $dumpFileName`;
  
　　$hd = fopen($dumpFileName, 'rb');
　　echo fread($hd, filesize($dumpFileName));
　　fclose($hd);  
?>