Abstract: The crack were found in the main drive shaft of an elevator during magnetic particle test after welding. The cracking causes of the elevator main drive shaft were analyzed by means of micro analysis, metallographic examination, mechanical property test and chemical composition analysis. The results show that the crack was located near the fusion line of heat affected zone of the elevator main drive shaft weld, which belong to liquefying crack near the weld caused by low melting eutectic products. The liquefying crack was caused by improper welding process.