Background <p>Bedtime procrastination is a prevalent self-regulation failure phenomenon among college students, linked to poor sleep quality and mental illness. There are many factors contributing to bedtime procrastination. Among them, self-compassion may alleviate it through its influence on emotional states, yet few studies have researched in-depth on this mechanism.</p> Methods <p>We conducted a three-wave longitudinal study with 7,174 Chinese college students (<i>M</i>_age = 19.11; 62.8% female) over an 8-month period. Self-compassion, positive affect, negative affect, and bedtime procrastination were measured at each wave. Cross-lagged panel modeling was used to examine temporal associations and indirect effects of self-compassion on bedtime procrastination through affective states.</p> Results <p>Significant correlations among self-compassion, positive affect, negative affect, and bedtime procrastination at different waves were observed (all <i>p</i> &lt; 0.001). Self-compassion predicted reduced bedtime procrastination over time both directly (<i>β</i> = −0.051, <i>p</i> &lt; 0.001) and indirectly via increased positive affect (<i>β</i> = −0.007, <i>p</i> &lt; 0.001) and decreased negative affect (<i>β</i> = −0.005, <i>p</i> &lt; 0.001).</p> Conclusions <p>This study provides the first longitudinal evidence that both positive and negative affect mediate the association between self-compassion and bedtime procrastination. These findings support emotion regulation as a key mechanism linking self-compassion to adaptive sleep behavior. Enhancing self-compassion may be a promising target for interventions aimed at reducing bedtime procrastination and improving sleep health among university students.</p>