Abstract: The male rotor fracture occurred during the starting process of screw compressor in the oil product unit of certain refinery.This paper makes an analysis on the macroscopic examination,chemical composition,metallographic examination,hardness testing and operating conditions of the fractured male rotor.The results show that the heat treatment of the male rotor didn＇t meet the design requirements.Because of abrasion,Laser cladding was carried out on the surface before the fracture of the male rotor and cracking appeared on the Laser cladding layers.During operation,the cracking expanded and led to fatigue fracture of the male rotor.According to the fracture causes,the paper puts forward the corresponding suggestions for improvement.