The ablation mechanism of spiral bevel gear material 20CrMnTi and the ablation characteristics of tooth surface by monopulse femtosecond laser at different energy densities are studied. Considering the dynamic energy absorption effect of material and mutual coupling interaction of photon-electron-lattice system， the energy coupling model is established. The simulation results show that the energy density of ablated gear material is at least 67 mJ/cm²， and the material removal occurs in the area within the ablation depth 40 nm. Experimental results show that when the tooth surface temperature exceeds the vaporization temperature of gear material， a good ablative morphology of tooth surface can be maintained， and the variation value of roughness is less than 0.021 μm， which verifies the effectiveness of theoretical simulation. These results could provide a reference for improving the tooth surface quality of spiral bevel gear with micro-precise machining of femtosecond laser.