Numerous studies have suggested that academic stress has negative impact on adolescents' psychological function, few of those studies, however, considered whether and how the impact of stress on adolescents' emotional states is moderated by corresponding regulation. This study aimed to examine the fluctuation of emotional states before and after the mid-term examination and the influence of different emotional regulatory strategies. In the present study, 72 adolescents aged 12-18 reported their emotional states and corresponding regulation before and after mid-term examination up to six times over a period of two weeks. Results showed that: (a) On the sampling day, the participants reported increasingly emotional states as time went by. Improvement of adolescents' daily emotional states was more significant after the mid-term examination. Participants reported decreasingly positive emotional states and increasingly negative ones as time went by before mid-term examination. (b) Adolescents who used down-regulation at a certain sampling moment reported more pleasant emotional states at the subsequent sampling moment than those who used up-regulation. Adolescents who used more up-regulation in a negative emotional event reported more negative emotional states at the subsequent sampling moment after the mid-term examination.