Cybervictimization has been shown to relate to suicidal ideation. However, few studies have fully clarified the directionality of this relationship, and little is known about the potential mediating and moderating mechanisms of this relationship. To address these gaps, the current study tested bidirectional relationships among cybervictimization, hopelessness, and suicidal ideation across three years using a cross-lagged design and examined whether these relationships varied by openness, family socioeconomic status, perceived economic stress, and sex. A total of 2,407 Chinese adolescents (50.23% female, Mage = 12.75, SD = 0.58 at baseline) from seven schools participated in the present study. The results indicated that cybervictimization was related to hopelessness and suicidal ideation. There was a vicious cycle between cybervictimization and hopelessness after controlling the effects of cyberbullying at T1. There were significant reciprocal relationships between hopelessness and suicidal ideation. Hopelessness at T2 mediated the relationship between cybervictimization at T1 and suicidal ideation at T3. Openness moderated the relationships among cybervictimization, hopelessness, and suicidal ideation. Family socioeconomic status, perceived economic stress, and sex did not play a moderating role. These findings will help to understand that intervening with hopelessness is a promising way to reduce adolescents’ cybervictimization and suicidal ideation, and promoting adolescents’ openness is an effective approach to alleviate the negative outcome of cybervictimization.