On the basis of traditional two-temperature model, a three-dimensional two-temperature model considering the variable defocus effect and the dynamic absorptivity effect with electron temperature was established. The changes of electron and lattice temperatures and the morphology of the pits during ablation were analyzed. The results of femtosecond laser ablation experiment on the surface gear material 18Cr2Ni4WA showed that with the increase of single pulse femtosecond laser energy density, the peak electron temperature increased, and the depth and diameter of the ablation pits increased continuously. The pulse width of single pulse femtosecond laser had no significant effect on the ablation morphology. The diameter and depth of ablative pits did not increase with the number of pulses, and the number of pulses had a threshold, beyond which the morphology of pits was adversely affected.