Using a three-wave longitudinal design, we examined the relationship between early parent-child relationship and subsequent smartphone addiction (SA) and explored mediating and moderating mechanisms underlying this relation. A total of 527 Chinese adolescents (271 boys and 256 girls, mean age = 11.23 years) completed questionnaires regarding parent-child relationship, smartphone addiction, hope and life satisfaction. The results showed that: (1) parent-child relationship (T1) was positively associated with life satisfaction (T1) and hope (T2); parent-child relationship (T1), life satisfaction (T1), and hope (T2) were significantly negatively associated with SA (T3); (2) After controlling for age, gender, and SA (T1), hope (T2) completely mediated the relationship between parental-child relationship (T1) and adolescents' SA (T3); (3) life satisfaction (T1) moderated the association between parent-child relationship (T1) and hope (T2). Specifically, as life satisfaction (T1) increased, parent-child relationship (T1) was more likely to promote hope (T2). Moreover, the indirect negative links between parent-child relationship (T1) and SA (T3) via hope (T2) were stronger for adolescents with high level of life satisfaction (T1) than for adolescents with low level of life satisfaction (T1). The results reveal the mechanism of hope and life satisfaction in the effect of parent-child relationship on SA in adolescents, indicating that SA among adolescents can be weakened through the improvement of parent-child relationship, the rise in hope and the increase in life satisfaction.