The three dimensional unsteady cooling process of flat steel is simulated by the numerical simulation calculation method of Finite Element Coupling Field. Then, the influential rules, which about layout parameters of the controlled cooling nozzle such as the distance and number of nozzle rows on the cooling effect, are analyzed separately. The results show that the distance of nozzle has a little effect on cooling rate. Relatively the number of nozzle rows affects cooling rate of flat steel greatly. Different layout parameters of the controlled cooling nozzle will be used by considering different factors. The numerical simulation results provide references for the layout of steel nozzle and controlled cooling device.