Objective: To explore the influence of social media usage on subjective well-being among college students in the context of COVID-19, and the mediating effect of anxiety on them. Methods: The questionnaire was compiled by social media usage scale, the index of well-being’s scale and self-rating anxiety scale. It was distributed in a university in Dongguan by handy sampling and snowball sampling method. The 242 valid questionnaires were analyzed by SPSS, including descriptive analysis, correlation analysis and regression analysis. Results: (1) Social media usage is significantly positively correlated with anxiety and subjective well-being, and anxiety is significantly negatively correlated with subjective well-being. (2) Anxiety plays a partially mediating role in the relationship between social media usage and subjective well-being. Conclusion: Social media usage can directly and positively affect subjective well-being, and also can affect subjective well-being through anxiety.