Abstract: In order to research the effect of laser cleaning pretreatment on the welding quality of 30 Cr3 ultra-high strength steel,surface morphology,element composition and matrix microstructure were observed by scanning electron microscope before and after cleaning. The results showed that the proper laser cleaning process could effectively remove the oxide layer on the surface of 30 Cr3 ultra-high strength steel,which made the surface smoother without damaging the base material. The test samples after laser cleaning were welded by electron beam. After welding,it was observed that the weld surface was well formed without undercut,depression and other defects,and the internal quality and mechanical properties of the weld fulfilled the requirements. Then welded joints were made into metallographic specimen to observe its microstructure and morphology.After laser cleaning pretreatment,welded joints were fully formed without crack,undercut and other defects under low power mirror. Through high power observation,grains in the center of the weld were fine and uniform. Therefore,the laser cleaning pretreatment of 30 Cr3 ultra-high strength steel could effectively remove the contaminated layer on the surface,and the welding quality met the requirements.