Objective. The study aims to explore the correlation mechanism among metacognition, attitude toward physical exercise, and health-related behavior in high school students. Methods. A total of 869 students (17 ± 1.70) from Anhui, Zhejiang, Shandong, and Fujian provinces were selected by stratified sampling to complete the Metacognition Questionnaire, Health-Related Behavior Self-Rating Scale, Attitude Toward Physical Exercise Scale, and Depression-Anxiety-Stress Scale (Simplified Chinese version, DASS-21). Results. (1) Metacognition was negatively predictive of attitude toward physical exercise and health-related behavior (β = −0.236, P < 0.01; β = −0.239, P < 0.01) but positively predictive of negative emotion (β = 0.496, P < 0.01); (2) attitude toward physical exercise was positively predictive of health-related behavior (β = 0.533, P < 0.01) but negatively predictive of negative emotion (β = −0.336, P < 0.01); and (3) negative emotion was negatively predictive of health-related behavior (β = −0.389, P < 0.01). Conclusions. Metacognition not only has a directly predictive effect on health-related behavior but also predicts it through attitude toward physical exercise. Negative emotion also mediates the relationship between metacognition and attitude toward physical exercise.