Previous research has provided limited exploration into the antecedents and mechanisms of academic expectations. Combining the broaden-and-build theory of positive emotions, this paper presents two investigations to examine the relationship between adolescents' academic emotions and academic expectations, as well as their underlying mechanisms. In Study 1, a questionnaire was distributed to 326 adolescent participants. The results indicated that adolescents' academic emotions influenced their academic expectations through their perception of teacher warmth and competence. Positive academic emotions improved participants' perception of teacher warmth and competence, thereby increasing their academic expectations. Conversely, negative academic emotions diminished perceived teacher warmth and competence, resulting in lower academic expectations. In Study 2, a situational experiment was used to manipulate the induction of positive or negative academic emotions with 145 adolescent participants using a one-way between-subjects design. The findings validate the mediating role of perceived warmth and competence. This research expands the theoretical foundation and holds practical significance. Future research can develop new experimental paradigms or explore alternative mechanisms based on this study.