Abstract: Lasers with wavelengths of 532 nm, 355 nm and 266 nm are obtained using harmonic generation of a Nd: YAG solid-state laser by nonlinear optical crystal. The relationship between the absorption of single crystal silicon and the laser wavelength and ablation characteristics of single crystal silicon by 3 different wavelength lasers under vacuum condition are studied. The results show that single crystal silicon has a good absorption of ultraviolet laser in the wavelength range of 100- 370 nm, and under the same conditions, the minimum single pulse energy for 532 nm laser ablation of silicon is 30 J and the minimum single pulse energy for 355 nm or 266 nm laser ablation of silicon is 15 J. The ablation threshold values of 532 nm, 355 nm and 266 nm laser ablation of silicon are different, which become smaller with the decrease of wavelength.