代码如下：

$zipfile=new ZipArchive();

            $upgradeFile=__SITEROOT.'_cache/update_'.date('Ymd').'.zip';

            if ($zipfile->open($upgradeFile, ZipArchive::CREATE | ZipArchive::OVERWRITE) === true){

                //设置密码 注意此处不是加密,仅仅是设置密码

                $zipfile->setPassword('12345678');

                foreach ($fileData as $k=>$v){

                    if ($v != '.' && $v != ".." && is_file($upgradePath . $v)) {

                        $zipfile->addFile($upgradePath . $v, $v);

                        //需要设置这句，加密密码才会生效

                        $zipfile->setEncryptionName($v,ZipArchive::EM_AES_256);

                    }

                }

            }

            $zipfile->close();

            if (file_exists($upgradeFile)){

                header("Cache-Control: public");

                header("Content-Description: File Transfer");

                header('Content-disposition: attachment; filename='.basename($upgradeFile)); //文件名

                header("Content-Type: application/zip"); //zip格式的

                header("Content-Transfer-Encoding: binary"); //告诉浏览器，这是二进制文件

                header('Content-Length: '. filesize($upgradeFile)); //告诉浏览器，文件大小

                @readfile($upgradeFile);

                @unlink($upgradeFile);

            }