Abstract: Boiler pressurized combustion is a serious problem,which affects theworking safety of the boiler. There are many factors in the problem. A caseof pressurized combustion is presented, which is caused by the unsteadyshedding flow of separated vortex in the forward and backward facing stepflow. Vibration of the wall caused by flow-solid coupling is anotherimportant factor causing pressurized combustion. A better result isachieved and electric power is saved with the wall being reinforced and theback facing step eliminated.