Directing aganst the serious slagging problem in boilers of a power plant, the causes leading to slagging in boilers have been analysed through measuring the behavior and slagging tendency of the fuel coal, as well as carrying out the computer numerical simulation. And a scheme for preventing boilers from slagging has been put forward from the view point of operation, stopping the primary air flow in the third level, deflecting the secondary air flow downward and so on.