按照phalcon官网的配置，配了一个：

server {
    listen      80;
    server_name localhost.portal;
    root        /var/www/portal/public;
    index       index.php index.html index.htm;
    charset     utf-8;

    location / {
        try_files $uri $uri/ index.php?_url=$uri&$args;
    } 
 
    location /public/ {
        root /var/www/portal;
    } 
    location ^~ /api/ {
       root /var/www/portal;
        rewrite  ^/api/(.*)$ /api/index.php?_url=/$1 last; 
   }
 
    location ~ \.php$ {
        try_files     $uri =404;

        fastcgi_pass  127.0.0.1:9000;
        fastcgi_index /index.php;

        include fastcgi_params;
        fastcgi_split_path_info       ^(.+\.php)(/.+)$;
        fastcgi_param PATH_INFO       $fastcgi_path_info;
        fastcgi_param PATH_TRANSLATED $document_root$fastcgi_path_info;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }

    location ~ /\.ht {
        deny all;
    }
}

其他url都能正常访问，可是访问api目录下的文件就会报404，api访问的目录依然是全局root目录：/var/www/portal/public，location里单设的root：/var/www/portal不生效。原因是：api路径 rewrite之后，再次访问生效的是location ~ .php$ {}配置，而这个配置继承的是全局的root。
修改为：不设全局的root，放到每个location里自行设置
把 location ~ .php$ {} 放到每个location里嵌套，就可以正常访问了。

server {
    listen      80;
    server_name localhost.portal;
    index       index.php index.html index.htm;
    charset     utf-8;
    rewrite_log on;
    access_log  /var/log/nginx/portal_access.log main;
    error_log   /var/log/nginx/portal_error.log notice;

    location / {
        root  /var/www/portal/public;    
        try_files $uri $uri/ /index.php?_url=$uri&$args;
        location ~ \.php$ {
            try_files     $uri =404;

            fastcgi_pass  127.0.0.1:9000;
            fastcgi_index /index.php;

            include fastcgi_params;
            fastcgi_split_path_info       ^(.+\.php)(/.+)$;
            fastcgi_param PATH_INFO       $fastcgi_path_info;
            fastcgi_param PATH_TRANSLATED $document_root$fastcgi_path_info;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        }   
    } 
 
    location /public/ {
        root /var/www/portal;
    }
 
    location ^~ /api/  {
        root /var/www/portal;
        rewrite  ^/api/(.*)$ /api/index.php?_url=/$1 last; 
        location ~ \.php$ {
            try_files     $uri =404;

            fastcgi_pass  127.0.0.1:9000;
            fastcgi_index /index.php;

            include fastcgi_params;
            fastcgi_split_path_info       ^(.+\.php)(/.+)$;
            fastcgi_param PATH_INFO       $fastcgi_path_info;
            fastcgi_param PATH_TRANSLATED $document_root$fastcgi_path_info;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        }
    }
 

    location ~ /\.ht {
        deny all;
    }
}