Why does it download by default when opening a web page?

<code>    server {
        #sitename    dev.wei.ui
        listen       80;
        server_name  dev.wei.ui;
        root         /server/htdocs/weui-master;
        error_log    /server/web/logs/nginx/dev.wei.ui-error.log;
        access_log   /server/web/logs/nginx/dev.wei.ui-access.log;
        autoindex    on;
        index        index.php index.html index.htm;

        location ~* ^.+\.(bak|inc|lib|sh|tpl|lbi|dwt|sql)$ {
             deny  all;
        }

        location ~ .*\.php?$ {
            fastcgi_pass   127.0.0.1:9002;
            fastcgi_index  index.php;
            fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
            include        fastcgi_params;
        }

        location / {
            if (!-e $request_filename) {
                rewrite  ^(.*)$  /index.php?s=$1  last;
                break;
            }
        }
    }</code>