The forced convective heat transfer coefficients during the period of thermal recovery for laser slab on the multi-segment amplifies of SG II is analyzed. We simulate the parameters including coolant gas and the geometry of amplifier with computational fluids dynamics (CFD) method. Based on the simulated results, we attain the optimized parameters such as the flow rate, the temperature and the type of gas, the diameter of inlet jet, the quantity of inlet jet, the distance between the inlet jet and the laser slab, and the spray angle of inlet.