Continuous improvement of farmers’ subjective well-being is an inherent requirement of rural revitalization and an essential part of common prosperity. Based on the happiness economics theories and the data from the China Labor Dynamics Survey (CLDS), this paper analyzed the impacts of the adoption of socialized service of agricultural machinery on farmers’ subjective well-being by the ordered Probit model and the intermediary effect model and discussed its mechanism and intergenerational heterogeneity. Results show that 64% of farmers choose to adopt the socialized service of agricultural machinery and 51% of farmers feel relatively happy or very happy, showing that there is a lot of room for improvement in the subjective well-being of farmers. The adoption of socialized service of agricultural machinery is conducive to improving farmers’ subjective well-being and results are still robust after using the endogenous transformation model and replacing the core variable test. From the perspective of mechanism, the socialized service of agricultural machinery can improve farmers’ subjective well-being by promoting non-agricultural employment. In addition, heterogeneity analysis shows that there is intergenerational heterogeneity in the impacts of socialized service of agricultural machinery on the subjective well-being of farmers, which significantly improves the subjective well-being of the older generation farmers, but no significant impacts on the subjective well-being of the new generation farmers. Accordingly, this paper proposes to vigorously support the development of socialized service of agricultural machinery, to promote the development of socialized service of agricultural machinery in the direction of specialization and standardization, to guide the connection between supply and demand of socialized service of agricultural machinery, and continuously to promote the improvement of farmers’ subjective well-being.