Abstract: The author has analyzed the quality problem of a certain type of marine diesel engine inlet valve seat on the shrinkage defects in the production process. The shell of the production process and the casting technology of casting was analyzed and found out the causes of the shrinkage defects. In the end, we presented these improvement measures: the first measure is to use red shell casting and appropriately reduce the cooling speed.; the second one is to adjust the metal liquid melt temperature and pouring temperature; the third one is to increase the inside sectional area; the fourth one is to increase the circular radius located between the runner and the valve seat ring cavity. The results show that the ratio of shrinkage defects decreased from about 12 percent to below 0.5 percent on account of improved production technology.