Thick walled casting is made of high alloy steel, and it has a concentrated thermal center because of its bigger difference of wall thickness, thus, the shrinkage defects are easy to appear at the hot spot in the casting process. The material and structure of the casting was analyzed. The casting process of a factory was simulated and the reasons for the generation of the casting defects were analyzed. Then, the measures were improved in order to optimize the casting process. The results show that when adop...