The blind holes processing experiment is conducted on the silicon under the radiation of a 355 nm nanosecond UV repetitive pulse laser. With the increase of the laser pulse number, the variations of the silicon morphology,the depth and aperture of the blind holes are observed, and the thermodynamic process of UV laser irradiating silicon is analyzed. The results show that the formation of the blind silicon hole in the laser ablation process is due to the interaction between thermal effect and force effect. Thermal effect results in fusion, vaporization and even producing laser plasma by ionization in silicon, which is essential to the removal of the material. The molten material is compressed by the plasma shock wave and the expansion of the high-temperature gaseous material,and then ejection outward, which will benefit the further ablation; the force propagates along the laser transmission direction,perpendicular to the silicon surface, so the removal parts are distributed mainly along the depth direction of the hole, reaching a high aperture ratio, which is up to 8:1 in our experiments. In addition, the laser-induced plasma also prevents the effect of laser on the target surface, and with the increase of hole depth, laser defocusing occurs. The two aspects finally restrict the ablation depth. The results shows that in the process of laser irradiation on the material, the ablation efficiency is much higher when the former 100 pulses arrived than the sequent laser pulses.