really thx for reply~

I understand the scenario is qtsql did not find qsqlmysql4.dll plugin.

my confussion is: Why? i've already put this plugin in the same path as execution file. and also in "C:\QT\4.6.2-vc\qt\plugins\sqldrivers" which is same as my developement pc.

Why the plugin would be found if the execution file using qtsql is build as a normal application but not a "qtservice " application?

P.S. the service application is launch by qtservicecontroller or system service control panel (after service installed) but NOT directly execute.