Background <p>Given the high prevalence of social anxiety among college students and its multifaceted negative impact on mental health, understanding its underlying mechanisms is critically important.</p> Methods <p>A three-wave longitudinal study was conducted with 4,846 Chinese college students (M_age = 18.98 years, 51.3% female) over a one-year period. The Random Intercept Cross-Lagged Panel Model (RI-CLPM) was used to examine bidirectional relationships and mediating effects.</p> Results <p>At the within-person level, significant bidirectional positive associations were observed between parent-child alienation and interpersonal sensitivity (<i>β</i> ranging from 0.094 to 0.114, <i>p</i> &lt; 0.001), as well as between interpersonal sensitivity and social anxiety (<i>β</i> ranging from 0.093 to 0.143, <i>p</i> &lt; 0.01). Parent-child alienation significantly and positively predicted subsequent social anxiety (<i>β</i> ranging from 0.087 to 0.095, <i>p</i> &lt; 0.01), while the predictive effect of social anxiety on subsequent parent-child alienation was marginally significant (<i>β</i> ranging from 0.049 to 0.051, <i>p</i> = 0.048–0.050). Interpersonal sensitivity acted as a bidirectional longitudinal mediator between parent-child alienation and social anxiety. Multi-group analysis revealed significant gender differences, with females showing higher autoregressive stability in interpersonal sensitivity and social anxiety, as well as stronger cross-lagged effects from interpersonal sensitivity to both parent-child alienation and social anxiety.</p> Conclusion <p>There is a complex bidirectional dynamic among parent-child alienation, interpersonal sensitivity, and social anxiety, with interpersonal sensitivity serving as a key bilateral mediator. These findings clarify the reciprocal influences between the family environment and individual cognitive-affective traits, offering valuable insights and practical implications for the prevention and treatment of social anxiety among college students.</p>