By means of chemical analysis, tensile test, metallographic analysis, and energy spectrum analysis, the leakage causes of seamless steel pipe in the process of pipeline pressure test were analyzed. The analysis shows that the crack of steel pipe appears before rolling, and the non-metallic inclusions near the crack are the crack source or preferred path of steel pipe cracking. The leakage of steel pipe defects in the subsequent eddy current and ultrasonic inspection is one of the main reasons the unqualified steel pipe flows into the construction site and leads to the leakage of the pressure test.