<p>Bedtime procrastination represents a critical threat to sleep health, with a rising prevalence. It is essential to identify the factors that influence bedtime procrastination in order to address this issue effectively. Previous research has identified security and Internet usage as factors that influence sleep quality. However, there is a lack of research exploring the influence of them on bedtime procrastination. Therefore, this mixed-methods sequential explanatory study intends to explore the relationship between college students’ security and bedtime procrastination, considering the potential mediation of nighttime Internet usage. In the quantitative phase, Security Questionnaire, Nighttime Internet Usage Survey, and Bedtime Procrastination Scale were administered to a sample of 769 Chinese college students recruited from an online survey platform, data was analyzed using a mediation model. Findings suggest that security negatively affects bedtime procrastination(<i>95%CI</i>=[-0.17,-0.07],<i>p</i> &lt; 0.001), and nighttime Internet usage mediate this relationship (<i>95%CI</i>=[-0.06.-0.02],&#xa0;<i>p</i> &lt; 0.001). During the qualitative phase, in-depth interviews with 15 participants who engage in surfing the internet before bedtime and has low level of security were conducted. These interviews highlighted that a lack of security prompted students to extend their nighttime Internet usage out of escapism and compensation motives, subsequently leading to bedtime procrastination. On the one hand, college students escape from experiencing negative mood and rumination by scrolling their phone. On the other hand, they compensate social needs by pre-sleep social media usage and online chatting.This study underscores a novel perspective on understanding bedtime procrastination and offers theoretical insights for intervention strategies.</p>