BackgroundPrevious studies on bedtime procrastination mainly focused on the influencing factors of stress and draw less attention on the role of family environment.AimThis study aimed to explore the effect of psychological stress reaction on bedtime procrastination in young adults, with considering the mediating effect of smartphone addiction, and the moderating effect of family cohesion during the COVID-19 pandemic.MethodsA sample of 1217 young adults completed psychological stress reaction scale, Smartphone addiction tendency scale for young adults, bedtime procrastination scale and family cohesion scale. A moderated mediation model was conducted to clarify the effect of psychological stress reaction on bad bedtime procrastination in young adults.ResultsThe findings showed that: (1) The individual level of psychological stress reaction was positively associated with bedtime procrastination; (2) Smartphone addiction mediated the effect of psychological stress reaction on bedtime procrastination; (3) Family cohesion moderated the relationship among psychological stress reaction, smartphone addiction and bedtime procrastination.ConclusionsThis study revealed the effect of smartphone addiction on the relationship between psychological stress reaction and bedtime procrastination during the COVID-19 pandemic, and these findings could provide novel evidence that family cohesion may serve as a protective factor against the negative consequences of smartphone addiction on bad bedtime procrastination.