This paper simulates the economic effects of trade liberalization in agricultural products between China and Japan under RCEP using the single market partial equilibrium analytical model (WITS-SMART). The results indicate that the trade creation effects of all agricultural products between China and Japan outweigh the trade transfer effects, and an increase in tariff reduction significantly enhances trade effects; although tariff revenues for China and Japan will be declined, the overall welfare of both countries will be improved, particularly with the largest welfare effects stemming from reduced tariffs in the cultivation sector. As the degree of tariff reduction intensifies, welfare effects expand; the advantageous agricultural products of both countries gain more opportunities through tariff reductions, with notable trade and welfare effects observed for Chinese products such as malt and pickled fish, while cereal and tobacco products face increased competitive pressure. This research provides policy considerations for better addressing the opportunities and challenges of agricultural trade liberalization between China and Japan under RCEP.