This study explored the relations between children’s intergenerational emotional support and subjective well-being (SWB) among Chinese middle-aged (45–60 years old) and elderly people (over 60 years old) and the mediation effect of the sense of social fairness between such associations. Using the 2017 Chinese General Social Survey dataset, a nationally representative survey, we selected 2413 middle-aged and elderly people who are 45 years and older, who suited the study requirements with 1097 males and 1316 females, which accounts for 45.5% and 54.5%, respectively. The average of age was 61.62 years old (SD = 10.45). The mediation analyses were conducted by multivariate regression and the SPSS macro PROCESS program. The results indicated that there was a significant association between children’s intergenerational emotional support and subjective well-being of middle-aged and elderly people (β = 0.0819, p < 0.001). Children’s intergenerational emotional support also had an indirect impact on subjective well-being through one path: the mediating role of the sense of social fairness (0.012). Direct effect (0.0699) and mediation effect (0.012) accounting for the total effect proportion was 85.35% and 14.65%, respectively. The findings may offer some meaningful implications for improving subjective well-being of middle-aged and elderly people. Future research should pay attention to the aforementioned factors with more detailed and comprehensive studies.