<p>Social media is gradually becoming an indispensable part of daily life for young people, making exploring its impact on their psychological well-being crucial. This study constructs a research model based on the Stressor-Strain-Outcome theory, collects data through a questionnaire survey, and uses a structural equation model to test hypotheses. The focus is on investigating how young people’s behavior on WeChat Moments influences their Subjective Well-being, along with potential mediating factors and pathways. The study finds that Use Intensity has a significant negative impact on Social Media Fatigue, upward and parallel social comparisons have significant positive impacts on Social Media Fatigue, Social Media Fatigue significantly negatively affects Bonding Social Capital, and social capital significantly positively affects Subjective Well-being. Furthermore, Bonding Social Capital partially mediates between usage intensity and Subjective Well-being and fully mediates between Social Media Fatigue and Subjective Well-being, with no significant mediating effect of Social Media Fatigue observed. These findings highlight that while WeChat Moments can promote Subjective Well-being through the cultivation of Bonding Social Capital, excessive social comparisons can lead to fatigue, diminishing its positive effects. This study provides critical insights into the nuanced role of social media in shaping young people’s psychological health and underscores the importance of fostering meaningful social interactions while mitigating the adverse effects of comparison-driven fatigue.</p>