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. However, the self-sufficiency rate of edible vegetable oil has been declining, and there is an urgent need to guarantee a safe supply of edible oil. Rapeseed is an important oil crop in China and has the advantage of not competing with land-based staple foods. Promoting rice-rape rotation is important for enhancing the self-sufficiency of edible vegetable oils. To stimulate farmers’ willingness to adopt the rice-rape rotation model, the Chinese government has formulated a series of subsidy policies that have expanded the area of rice-rape rotation; however, studying the incentive effect on rapeseed yield is worthwhile. This study is based on the perspective of professional grain farmers, the core subject of rice and rapeseed production, and theoretically reveals the impact of rice-rape rotation subsidies on rapeseed yields of professional grain farmers and explores the impact of rice-rape rotation subsidies on rapeseed yields and its mechanism using the research data of 303 professional grain farmers in Jiangxi Province, and applied OLS linear regression, quantile regression, moderated mediation effect test and other methods to to explore the influence and mechanism of rice tanker subsidies on rape yield. This study has the following findings. First, the benchmark regression results show that the rice-rape rotation subsidy promotes rapeseed yield. The rapeseed yield increase by 2.38% with every 10% increase in the rice-rape rotation subsidy. The research conclusions still hold after applying the two-stage least squares method and approximating exogenous instrumental variables to address the endogeneity problem. Second, to further analyze the effect of the rice-rape rotation subsidy on the differences in rapeseed yield under different rotation ripening modes and rotation scales, the samples were divided into different subsamples, and group regression was carried out. The results showed that the rice-rape rotation subsidy had a more significant effect on the rapeseed yield of the farmers in the two-ripening rotation modes, while it did not significantly affect the farmers in the three-ripening rotation modes. The effect of the rice-rape rotation subsidy on the rapeseed yield of medium-sized farmers was more significant than that of large and small scale farmers. Third, 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 social networks positively regulated the relationship between the level of labor allocation within agriculture and rapeseed yield, thus improving the promotional effect of the rice-rape rotation subsidy on rapeseed yield. Therefore, governments at all levels should optimize the subsidy policy for rapeseed cultivation, strengthen the dynamic adjustment of crop rotation subsidies, and improve the management of rapeseed production.