Abstract: Maintaining the supply and price of important agricultural products is related to the overall situation of national development and security. At present, China’s food ration has achieved absolute safety, but the self-sufficiency rate of edible vegetable oil has been declining, and the task of guaranteeing the safe supply of edible oil is very urgent. Rapeseed is an important oil crop in China, which has the advantage of not competing with staple food for land. Promoting the rice-rape rotation mode is an important path to enhance the self-sufficiency level of edible vegetable oil. To stimulate the willingness of farmers to adopt the rice-rape rotation model, the Chinese government has formulated a series of subsidy policies, which have expanded the area of rice-rape rotation, but it is worthwhile to study the incentive effect on rapeseed yield. This paper is based on the perspective of professional grain farmer, the core subject of rice and rape production, theoretically reveals the impact of rice-rape rotation subsidies on rapeseed yields of professional grain farmer, and explores the impact of rice-rape rotation subsidies on rapeseed yields and its mechanism by using the research data of 303 professional grain farmers in Jiangxi Province, so as to provide scientific basis for the government to improve the rice-rape rotation subsidy policy. This study has the following findings: first, the benchmark regression results show that rice-rape rotation subsidy has a promoting effect on rapeseed yield. The rapeseed yield will increase by 2.38% with every 10% enhancement of rice-rape rotation subsidy. This study uses three robustness tests, namely, replacing the core explanatory variable, Winsorize treatment method, and quantile regression. The research conclusions still hold after the two-stage least squares method, and the method of approximating exogenous instrumental variables to deal with the problem of endogeneity. Secondly, in order to further analyze the effect of rice-rape rotation subsidy on the differences of rapeseed yield under different rotation ripening modes and different rotation scales, the samples were divided into different sub-samples, and group regression was carried out. The results showed that rice-rape rotation subsidy had a more significant effect on the enhancement of rapeseed yield of the farmers in two-ripening rotation modes, while it did not have a significant enhancement on the farmers in three-ripening rotation modes. The effect of rice-rape rotation subsidy on rapeseed yield of medium-sized farmers was more significant than that of large-scale farmers and small-scale farmers. Thirdly, the mechanism test was conducted by using Bootstrap method and KHB mediating effect decomposition method, and the mediating effect results showed that the level of labor allocation within agriculture played a partial mediating role in the path of rice-rape rotation subsidy affecting rapeseed yield, with the mediating effect contributing 34.88% of the weight. The results of the moderated mediating effect showed that the social network positively regulated the relationship between the level of labor allocation within agriculture and rapeseed yield, thus improving the promotion effect of rice-rape rotation subsidy on rapeseed yield. Therefore, governments at all levels should optimise the subsidy policy for oilseed rape cultivation, strengthen the dynamic adjustment of crop rotation subsidy, and cultivate the management main body of oilseed rape production.