The relationship between self-control and subjective well-being is far from conclusive. Some argue that self-control is positively correlated with subjective well-being because people high in self-control are more adaptive and more successful in their lives. Other scholars argue that people high in trait self-control may not be high in subjective well-being, as those people usually experience emotional cost for the sake of rational purpose in their goal-attainment processes. Past researches indicate that motivation is an important mediator in the relation between trait self-control and subjective well-being. According to regulatory focus theory, there are two motivational orientations which lead people to utilize different ways to pursue their goals, resulting in distinct experiences. As such, the present study aimed at exploring the role of the two motivational orientations in the relation between trait self-control and subjective well-being. Participants were college students who voluntarily took part in this research. They completed a package of questionnaires measuring their trait self-control, regulatory focus, positive and negative affect, and life satisfaction. The score of trait self-control, promotion motivation and prevention motivation directly obtained from the measurement of the corresponding scales. The scores of subjective well-being were the sum of the z-scores of positive affect and negative affect (recode score), as well as life satisfaction. The results showed that trait self-control was positively correlated with subjective well-being (β = .64), consistent with existing literature. Results also showed that both promotion motivation and prevention motivation were positively correlated with trait self-control and subjective well-being. Then we analyzed the mediating effects of promotion and prevention motivation in the relation between trait self-control and subjective well-being. The results showed that (1) the correlation between trait self-control and subjective well-being is reduced from .64 to .23; (2) promotion motivation positively correlate with both trait self-control (β = .44) and subjective well-being (β = .88), thus it partially mediated the two variables (effect size is .39 which accounted for 60.5% of the total effect); (3) prevention motivation was positively correlated with trait self-control (β = .31), but was not correlated with subjective well-being (β = .07). Thus the results from mediating analysis indicated that promotion motivation is a key variable influencing people’s subjective well-being. Further analysis showed that: (4) even controlling the effect of trait self-control, promotion-dominant people reported higher subjective well-being than prevention-dominant people; (5) people low in trait self-control but dominanted by promotion motivation had no difference in subjective well-being than people high in trait self-control but dominanted by prevention motivation. Taken together, the present study suggested that though trait self-control positively correlated with subjective well-being, as the role of motivation , people high in trait self-control even had the equal subjective well-being with people low in trait self-control. Thus the main contribution of this study is that these results further confirm the relationship between trait self-control and subjective well-being. More importantly, the present study provided evidence explaining why some people high in self-control were happier but some people high in self-control were not.