In order to investigate the mechanism of the influence of dysfunctional attitudes on positivity emotion ratio among college freshmen, this study took 400 freshmen in a university as the research subjects, and used the Positive Rate Self-assessment Scale, Self-esteem Scale, and Dysfunctional Attitudes Scale to measure them. The results showed that: (1) There is a correlation between dysfunctional attitudes, positivity emotion ratio and self-esteem among college students; (2) Self-esteem has a mediating effect in the influence of dysfunctional attitudes on positivity emotion ratio; (3) Self-esteem plays a fully mediating role between the autonomy factor and positive rate, while there is no mediating effect between the achievement factor and positive rate.