Energy poverty is a serious problem worldwide that negatively impacts the subjective well-being of elderly residents. This paper aims to explore this relationship. Firstly, based on 2011, 2013, 2015, and 2018 data of the China Health and Retirement Longitudinal Study (CHARLS) launched by Peking University for 125 prefecture-level cities, representing 32,490 observations, this paper effectively and multidimensionally measures the level of individual energy poverty. Secondly, a mediating model is adopted to study the causal effect between energy poverty and subjective well-being through the OLS and 2SLS methods using carefully selected instrumental variables to overcome potential endogeneity. Finally, through a variety of robustness tests, the stability of the above causal effects is verified. The results show that energy poverty negatively affects senior citizens’ subjective well-being. Health, depression level, and household food expenditure level can be used as the micro mechanism between the two variables. The above factors have a greater impact on those senior citizens with low educational backgrounds, from relatively low-income families, living alone, and having an urban household registration.