@taokai, root /home/wwwroot/default/dl;替換為alias /home/wwwroot/default/dl/;

worker_processes auto;

error_log /home/wwwlogs/nginx_error.log crit;

pid /usr/local/nginx/logs/nginx.pid;

#Specifies the value for maximum file descriptors that can be opened by this process.
worker_rlimit_nofile 51200;

events
{
use epoll;
worker_connections 51200;
multi_accept on;
}

http
{
include mime.types;
default_type application/octet-stream;

server_names_hash_bucket_size 128;
client_header_buffer_size 32k;
large_client_header_buffers 4 32k;
client_max_body_size 50m;

sendfile on;
tcp_nopush on;

keepalive_timeout 60;

tcp_nodelay on;

fastcgi_connect_timeout 300;
fastcgi_send_timeout 300;
fastcgi_read_timeout 300;
fastcgi_buffer_size 64k;
fastcgi_buffers 4 64k;
fastcgi_busy_buffers_size 128k;
fastcgi_temp_file_write_size 256k;

gzip on;
gzip_min_length 1k;
gzip_buffers 4 16k;
gzip_http_version 1.1;
gzip_comp_level 2;
gzip_types text/plain application/javascript application/x-javascript text/javascript text/css application/xml application/xml+rss;
gzip_vary on;
gzip_proxied expired no-cache no-store private auth;
gzip_disable "MSIE [1-6]\.";

#limit_conn_zone $binary_remote_addr zone=perip:10m;
##If enable limit_conn_zone,add "limit_conn perip 10;" to server section.

server_tokens off;
#log format
log_format access '$remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" $http_x_forwarded_for';
access_log off;

server
{
listen 81 default_server;
#listen [::]:81 default_server ipv6only=on;
server_name http://www.lnmp.org;
index index.html index.htm index.php;
root /home/wwwroot/default;

location /images {
root /home/wwwroot/default/dl;
autoindex on;
}

#error_page 404 /404.html;
include enable-php.conf;

location /nginx_status
{
stub_status on;
access_log off;
}

location ~ .*\.(gif|jpg|jpeg|png|bmp|swf)$
{
expires 30d;
}

location ~ .*\.(js|css)?$
{
expires 12h;
}

location ~ /\.
{
deny all;
}

access_log /home/wwwlogs/access.log access;
}
include vhost/*.conf;
}

@Dianso, 把你的配置文件發上來看一下