Background: Mental health problems of adolescents have escalated significantly in recent years, categorising this population as a high-risk group for suicide.Objective: This study aims to investigate the developmental trajectories of suicidal ideation among junior high school students in mainland China, as well as its influencing factors.Methods: Longitudinal data were collected in three-waves, with three-month intervals in Zhenjiang City. A valid sample of 129 students completed questionnaires on suicidal ideation, life events, perceived stress, psychological flexibility, and demographic information.Results: Unconditional latent growth models revealed a significant increasing trend in suicidal ideation, characterised by an initial gradual increase and an accelerated rise afterwards. Conditional latent growth models indicated that both life events and perceived stress elevated the level of suicidal ideation, whereas psychological flexibility did not.Conclusions: These findings have significant implications for the development of targeted prevention and intervention strategies for adolescent at risk of suicide, highlighting the need for early identification. Life events and perceived stress are key risk factors to consider. The findings also emphasise the importance of promoting psychological flexibility as a potential protective factor in reducing suicidal ideation.