In this paper, a double-temperature heat transfer model for the gear material 18Cr2Ni4WA is established in order to analyze the composition and morphological influence of femtosecond laser ablation surface of gear tooth surface. The numerical simulation of femtosecond laser ablation surface is carried out using backward finite difference method to study the machining process of femtosecond laser ablation surface, and the influence law of energy density on recast layer and heat-affected layer is analyzed. The results show that the energy density increases from 1.73 J/cm² to 4.33 J/cm², the thickness of recasting layer increases from 0.68 μm to 1.02 μm, and the thickness of heat affected layer increases from 0.96 μm to 1.35 μm. Aiming at the control of recast layer, a secondary machining of opposite gear tooth surface is implemented, and the experimental results show that when the energy density of 1.73J/cm² is used for secondary machining of the tooth surface, there is almost no recast residue; and the average roughness of the tooth surface decreases from 0.365 μm to 0.185 μm, which effectively improves the machining quality of the tooth surface gear, and provides a useful reference for improving the precision of femtosecond laser ablation surface gear.