Abstract: Cnaphalocrocis medinalis is an important migratory pest in rice production. In order to develop a compound pesticide suitable for seed treatment and effective long-term control of C. medinalis, the optimal ratio of chlorantraniliprole and monosultap, as well as the field control effect, was studied through indoor systematic action test, field effect verification, and pesticide residue detection in rice plant. The long-term prevention and control mechanism of the compound agent had been preliminarily clarified. The results from the systematic action test indicated that the highest co-toxicity coefficient and strongest systemic absorption occurred when the mass concentration ratio of chlorantraniliprole and monosultap was 2﹕3. The chlorantraniliprole + monosultap 25% seed treatment suspension concentrate (FS), including 10% chlorothalonil and 15% benzamide, was prepared at doses ranging from 7.5-15 g/kg (seeds). This formulation is safe for seed germination and seedling emergence. The field experiment showed that the application of chlorantraniliprole + monosultap 25% FS at 7.5-15 g/kg (seeds) significantly controlled C. medinalis in the rice field, maintaining effective leaf preservation for an extended period. Even after 94 days post-seeding, approximately 70% leaf protection effect was observed. The detection of pesticide content in rice plant showed that the sustained control capability of chlorantraniliprole + monosultap 25% FS against C. medinalis was primarily associated with the chlorantraniliprole content in the leaves. Although monosultap in the compound formulation degraded relatively quickly, its presence enhanced the absorption rate of chlorantraniliprole by rice roots during the seedling stage. This study can provide a theoretical basis and technical reference for the development the seed treatment agents for the control C. medinalis.