From the perspectives of positively adaptive and developmental goals, this study aims to establish the structure of positive mental health for middle school students and develop the Positive Mental Health Scale for middle school students. Firstly, an initial entry pool was established by combining literature search and expert interviews. Then, a total of 1488 students from junior and senior high schools in a middle school in Sichuan Province were selected to complete the scale, and the collected data was submitted into the psychometric property analyses of the scale. The results showed that the formal scale contained 24 items belonging to 4 dimensions — interpersonal harmony, scholastic competence, self-control and self-fulfillment, and the scale showed a series of good psychometric indexes. It is concluded that the Positive Mental Health Scale for middle school students is qualified to be used as an effective tool to assess the mental health of Chinese middle school students, which will contribute to promoting the mental health of middle school students. This scale has theoretical and practical implications for future research in related fields.