In order to improve the location of laser spot center accuracy in semiconductor laser processing, according to the gray distribution characteristics of spot image generated after picosecond ultra-short pulse laser irradiating monocrystalline silicon, an algorithm of laser spot center location based on gray histogram was proposed. Through simulation analysis of laser spot and monocrystalline silicon etching experiment, the positioning accuracy of the proposed algorithm was compared with that of the traditional algorithm under different irradiation time and laser power. Results show that under different irradiation times, the algorithm precision is 0.761 μm, 51.3% higher than that of gray centroid method and 93.9% higher than that of the maximum column gray value method. Under different laser power, the algorithm precision is 0.793 μm, 73.4% higher than that of gray centroid method and 86.8% higher than that of the maximum column gray value method. It can provide guidance for the design of the control system for spot center positioning of picosecond ultra-short pulse laser.