Objective: Internet-based cognitive behavior therapy (ICBT) may provide an accessible alternative to face-to-face treatment, but the evidence base in adolescents is limited. This systematic review and meta-analysis aims to comprehensively assess the efficacy of ICBT in addressing depression among adolescents. Methods: Four electronic databases were searched on June 8, 2023. Randomized controlled trials (RCTs) evaluating the efficacy of ICBT for depression in adolescents were included. The quality of the studies was assessed using the risk of bias tool recommended by the Cochrane Handbook. Furthermore, the GRADE approach was employed to gauge the certainty of the obtained evidence. Meta-analysis was conducted using RevMan 5.4, and Egger's test was implemented through Stata for assessment of potential publication bias. Results: A total of 18 RCTs involving 1683 patients were included. In comparison to control groups like attention control, waiting list, and treatment as usual, our meta-analysis findings elucidate a significant reduction in depression scores (SMD = -0.42, 95 % CI: [-0.74, -0.11], p < .05) as well as anxiety scores (SMD = -0.34, 95 % CI: [-0.60, -0.08], p < .05) in adolescents following ICBT interventions. Furthermore, the analysis indicated no notable distinctions in patient's quality of life (QoL) scores. (SMD = 0.12, 95 % CI: [-0.10, 0.34], p > .05). Conclusion: Results provide evidence of the efficacy of ICBT to reduce depressive and anxiety symptoms in adolescents. These research findings are of vital significance for the establishment of evidence-based treatment guidelines in the digital era. Trial registration: PROSPERO registration: CRD42021277562.