The invention relates to a method for modularizing a saddle sand mold. The method comprises the following steps: designing a saddle mold and preparing sand molds; cutting a casting mold into a first casting mold unit on the lower part and a second casting mold unit on the upper part, wherein the second casting mold unit comprises original four guide rail internal chamber cores requiring to be labeled and a jaw core; and printing the sand mold of each casting mold unit by 3DP adding material manufacturing equipment. According to the method provided by the invention, the inner chamber cores and the upper mold are connected with each other to form a whole body so as to form one casting mold unit integrally, no assembling is required, the casting mold unit is matched with the lower mold so as to form a complete cavity, the core labeling operation in the matching process of a saddle casting core in the prior art is avoided and the structural strength of the casting mold unit is ensured.