摸索了一会儿，先配置成功，再看看PATH_INFO之类的东东吧。
A，根目录：
location ~ \.php($|/) {
root html;
fastcgi_pass 127.0.0.1:9000;
fastcgi_index index.php;
fastcgi_split_path_info ^(.+\.php)(.*)$;
fastcgi_param PATH_INFO $fastcgi_path_info;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}
if (!-e $request_filename) {
rewrite ^(.*)$ /$1 last;
break;
}
B，子目录：
location /CI/ {
if (!-e $request_filename) {
rewrite ^/CI/(.*)$ /CI/index.php/$1 last;
break;
}
}
location /CI/index.php {
fastcgi_pass 127.0.0.1:9000;
fastcgi_split_path_info ^(.+\.php)(.*)$;
fastcgi_param PATH_INFO $fastcgi_path_info;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}