Abstract: A six-cylinder crankshaft was found to have cracks on the surface of the fifth connecting rod neck during the flaw detection process of the finished product.The crack was comprehensively analyzed by means of macro analysis, micro analysis, energy spectrum micro area composition analysis and so on.The results show that the crack is caused by residual shrinkage holes in the raw material, which extend to the surface after the subsequent rolling, forging and quenching process.