php pgadmin远程数据库连接失败

我想连接到从php到postgres的远程数据库，但它无法连接并说

 Warning: pg_connect() [function.pg-connect]: Unable to connect to PostgreSQL server:    
could not connect to server: No route to host (0x00002751/10065) Is the server running on host "xxxxxxxxx" and accepting TCP/IP connections on port 5432? in C:xampphtdocstest.php on line 4
Wrong CONN_STRING

<html> 
    <body> 
        <?php 
        $db = pg_connect('host=xxx.xxx.xxx.xxx port=5432 dbname=postgres user=postgres password=') or die('Wrong CONN_STRING'); 
        if (!$db) {
                echo 'error';
            }else{
            echo 'success';
            }

        ?> 
    </body>

我可以从运行apache的同一台机器上运行的pgadmin客户端访问同一个数据库，我无法理解pgadmin可以访问db但是apache webserver的php无法访问？任何的想法？