Single-pulse separated ablation and multi-pulse cumulative ablation experiments are performed on single crystal diamond by femtosecond laser with different powers. The single-pulse ablation threshold and multi-pulse cumulative ablation threshold of single-crystal diamond materials are calculated, and the variation characteristics of ablation threshold of single-crystal diamond at multi-pulse are studied. The results show that the threshold of femtosecond laser ablation of single crystal diamond is 8.80 J/cm 2. The ablation threshold of single crystal diamond materials decreases with the increase of effective pulse number. When the effective pulse number is less than 124, the ablation threshold decreases sharply with the increase of the effective pulse number. When the effective pulse number increases to 486, the decreasing trend of ablation threshold tends to be gentle. The optimum laser processing parameters are as follows: the effective pulse number is 486, and the laser average power is 10.7 W.