Abstract: Engineering 45 steel has good toughness, plasticity and high strength, and has become one of the preferred materials for manufacturing shaft parts and transmission parts (such as gears, etc.). Complex and diverse rod, shaft, bolt parts and other processing technology, such as turning, hot forging, cold heading, heat treatment, etc., the surface quality and mechanical properties of round steel are high requirements, especially some shaft parts require high hardness and strength. Therefore, in order to improve the performance of engineering 45 steel, the surface modification treatment of engineering 45 steel samples was carried out by using hundred-picosecond laser shock peening technology, and the influence of laser shock peening on the morphology and performance of the samples was investigated. Laser shock peening is a new material surface modification technology, which has many outstanding advantages such as non-contact, no heat affected zone and strong controllability. Compared with traditional technology, it has better strengthening effect, stronger controllability and better applicability. Laser shock peening plays an important role in improving structural reliability and component fatigue strength and prolonging material service life. The effects of laser energy, spot bonding rate and impact times on the microstructure and mechanical properties of the surface layer of the material were determined by comparative experiments, and the best experimental parameters were obtained. The surface morphology, microstructure, roughness and hardness properties of materials after laser shock were evaluated by digital microscope, 3D profile measuring instrument, roughness tester and hardness tester, and the internal mechanism was analyzed. The results are as fowows. 1) The surface of the sample can be enhanced with different degrees of macroscopic pits, and the microstructure of the sample can be changed. With the increase of laser energy, spot bonding rate and laser shock frequency, the degree of macroscopic pits and microscopic grain refinement of the sample are deepened. 2) Hundred-picosecond laser shock peening can increase the surface hardness of the sample and produce a hardened layer, while improving the roughness of the sample. In addition, the laser energy, spot bonding rate and laser shock frequency have regular effects on the hardness and roughness. 3) Through the analysis and comparison of the test data, the optimal parameters of laser shock in this hundred picosecond laser shock experiment are 70% spot bonding rate, 1 shock time, and 0.5 J laser energy. Under this condition, the maximum surface hardness of the sample is increased by 20%, and the deep hardness thickness reaches 1 mm. 4) High-energy pulses are used for impact strengthening on the surface of the material. In the impact process, a large number of high-density dislocations are generated on the surface, and the angles of each grain boundary change, thus forming critical subgrains. The further evolution results in the refinement of grain size. The impact strengthening provides the driving force for the recrystallization of the material, and then produces some properties and characteristics of the test material such as hardness and surface roughness. It can be seen that the laser shock peening experiment has achieved obvious results, which has reference significance for the surface modification of 45 steel materials and other metal materials.