This research aims to examine the relationship between social support and subjective happiness of middle school students, and the mediating effect of self-encouragement. we administrated a questionnaire on 388 middle school students. Correlation analysis and covariance structure equation model analysis were conducted for the data analysis. The results of this study are as follows. First, there is a positive correlation among social support, self-encouragement, and subjective happiness. Second, it was found that social support had a direct effect on the subjective happiness of middle school students. Friend support and family support among the subfactors of social support had a significant effect, but teacher support was not found to be significant. Third, self-encouragement had a partial mediating effect on the relationship between social support and subjective happiness. Friend support partially mediated subjective happiness through the paths of cognitive self-encouragement, behavioral self-encouragement, and emotional self-encouragement; and family support also showed a partial mediation on subjective happiness through the paths of cognitive self-encouragement, behavioral self-encouragement, and emotional self-encouragement. The limitations and suggestions of the future research were discussed in the end.