To solve the leakage problem during the sealing test of an aero-engine aluminum alloy casing formed by an embedded pipe, the mechanism of the leakage was analysed by micro/macro structure observation and digital X-ray real-time imaging (DR) technology, and then the solution measures were formulated. With the analysis of the structure and process characteristics, it is clear that the leakage is caused by the gap between the embedded stainless steel tube and the aluminum matrix and the metallurgical defects of the aluminum matrix. However, limited by the X-ray detection capability, this metallurgical defect cannot be identified by conventional nondestructive testing. Finally, the optimization of the casting process has been taken to solve the leakage problem of the casing.