<p>Previous studies have shown positive associations between economic hardship and technological addictions (i.e., internet addiction and smartphone addiction) among adolescents. However, the risk factors and psychological mechanisms may differ for specific mobile application addictions, and this possibility remains unexplored in the context of short-form video addiction. This study thus aimed to investigate the longitudinal association between perceived economic hardship and short-form video addiction among Chinese adolescents and to examine the mediating role of internalizing problems and externalizing problems as well as the moderating role of belief in a just world. A total of 1319 adolescents (53.4% female; <i>M</i>_age = 16.18) from three high schools in eastern China participated in a three-wave (called T1, T2 and T3) longitudinal study across six months. Results showed that T1 perceived economic hardship was positively associated with T3 short-form video addiction six months later. Results from longitudinal path analysis showed that T2 internalizing problems and T2 externalizing problems both mediated this association, and T1 belief in a just world mitigated the association between T1 perceived economic hardship and T3 short-form video addiction. The results further showed that the indirect effect of T1 perceived economic hardship on T3 short-form video addiction via T2 internalizing problems and T2 externalizing problems was significant only in adolescents with lower levels of T1 belief in a just world. Interventions targeting economic hardship and belief in a just world may be important in addressing short-form video addiction.</p>