The invention discloses a sand core coating preparation method for improving casting quality. The method comprises the following steps: S1, preparing a mixture A; S2, carrying out acid leaching treatment on the graphene nanosheets; S3, acylating the graphene nanosheets; S4, preparing a material B; S5, weighing raw materials; and S6, preparing the finished product paint. The preparation method is simple in overall process, reasonable in matching of all steps, low in production cost, safe and environment-friendly, and the prepared coating has good strength and impact resistance, is high in heatconductivity and not easy to crack, effectively improves the surface precision of a casting and improves the casting quality.