Abstract: According to the agreement standard and specification, discontinuities were discovered in 17-4PH stainless steel parts for military use with the help of magnetic particle testing. It is found that these liner indications, which are common in the same materials and have seriously effects on the judgments of the final magnetic particle testing results, were induced by chemical composition and microstructure segregation. The defect indications could either be reduced by heat treatment, or be avoided by improving gating system or radiation condition. Based on the results of liner indication on 17-4PH stainless steel castings, the reliability factors which affect magnetic particle testing have been discussed. It is hoped that the present test and analysis conclusion could be for reference for similar indications in magnetic particle testing of same material.