Background Physical activity (PA) can effectively reduce social anxiety (SA), which is currently one of the most effective forms of psychological intervention. This study explored the relationship between exercise frequency, intensity, duration and social anxiety.Methods This study was a college-based cross-sectional study. 844 college students from six universities in Qingdao, Shandong Province, China, were sampled for this study. The daily physical activity of the participants was assessed using the Physical Activity Rating Scale-3, While the social anxiety level was evaluated using the Liebowitz Social Anxiety Scale. A survey questionnaire was developed to investigate the essential characteristics of the participants. In addition, this study examined the relationship between physical activity components (frequency, duration, intensity) on motion features and social anxiety levels. Additional work was conducted to test if physical exercise played an alleviation role in mediating social anxiety levels in college students. Finally, moderation was analyzed using PROCESS macro for SPSS, and the relationship was evaluated by non-linear index fitting.Results The results revealed that the exercise intensity(I) (F = 24.35, p < 0.01), exercise frequency(F) (F = 16.31, p < 0.01), and exercise duration (D) (F = 9.8, p < 0.01) were significant differences correlated with the score of social anxiety. This post hoc analysis showed that the SA level of Frequency 1(F1) was significantly higher than that of Frequency 3(F3) and Frequency 5(F5), and the SA level of Intensity 1(I1) was substantially higher than that of Intensity 3(I3) and Intensity 5(I5). In addition, the SA level of Duration 1(D1) was significantly higher than that of Duration 3(D3) and Duration 5(D5). In addition, the total score of SA was negatively correlated with the total score of physical activity (p < 0.01).Conclusions Physical activity can alleviate social anxiety among university students. The most beneficial and optimized exercise plan: Moderate intensity, once or twice a week, and 21–30 minutes of exercise per session may reduce social anxiety.