Abstract: The drop of lifted body with a production safety accident was caused by the fracture of the variable-speed motor shaft of the large-sized gantry crane. The fracture causes of the variable-speed motor shaft were analyzed by using macroscopic-and microscopic analysis methods. The results showed that the immediate brittle fracture was triggered by local fatigue cracking and extending of variable-speed motor shaft in long-duration operation,and the fracture of the shaft was related to the low manufacturing quality and about fifty years active time.