我的appconfig这么些的:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>

<appSettings>

<add key="DBHost" value="JF023\\SQLEXPRESS" />
<add key="DBName" value="wage" />
<add key="DBUser" value="sa" />
<add key="DBPass" value="jfis" />
</appSettings>
<connectionStrings>

</connectionStrings>

</configuration>
在程序中调用：
public string Constr()
{
string dbhost = System.Configuration.ConfigurationManager.AppSettings["DBHost"];
string dbname = System.Configuration.ConfigurationManager.AppSettings["DBName"];
string dbuser = System.Configuration.ConfigurationManager.AppSettings["DBUser"];
string dbpass = System.Configuration.ConfigurationManager.AppSettings["DBPass"];
string connStr= "server="+dbhost+";database="+ dbname+";uid="+dbuser+";pwd="+dbpass+"";
return connStr;
}

为什么不行啊！