Abstract: By analyzing and improving the casting process of a multi-isolated hot-joint cast iron exhaust manifold,the waste rate of loose casting, cold isolation and peeling was reduced from 26% to 2%, and the technological yield of casting was also increased by 3%. The author describes the process of solving casting defects. It is proved by the case that the position of molten iron, riser position and placement of cold iron have a very important impact on casting defects. The correct design of molten iron position and the use of cold iron combined with riser is an important link to improve the yield of multi-isolated hot joint cast iron exhaust pipe casting, and it is also an important factor affecting the casting process yield.