Abstract: Taking the subframe longitudinal beam as the research object, through process analysis, the problem of poor mold filling of thin-walled products in the metal mold low-pressure casting process is solved. Due to the large overall dimension of the casting and the main wall thickness of 5 mm, poor mold filling defects are easy to appear in the process of metal mold low-pressure casting. According to the problems of poor filling type of casting, the factors affecting the filling ability of metal liquid were studied and analyzed, and the process scheme was optimized to meet the requirements of mass production.