Objective: To analyze the trends of Internet addiction among adolescents in Shanghai, so as to provide theoretical evidence for the prevention and control of Internet addiction in adolescents. Methods: A multistage stratified cluster random sampling method was conducted, and 92 171 junior and senior high school students in Shanghai were selected for questionnaire survey in 2004-2019. Evaluation of Internet addiction, loneliness, academic pressure and depression among middle school students. Results: In 2004-2019, the rate of Internet addiction among middle school students in Shanghai was 4.3%, which without significant differences by year( t =1.8, P >0.05). The detection rate of Internet addiction in boys (5.3%) was higher than that in girls (3.4%) ( χ 2=186.8, P <0.01), and was highest in secondary vocational school (7.7%), followed by senior high school (4.6%) and junior middle school students (2.8%) ( χ 2=746.5, P <0.01). The prevalence of Internet addiction in girls, senior high school students, secondary vocational school students, students aged 16-20, students with loneliness or high academic pressure showed an increasing trend in 2004-2019, with the average annual increase rate ( APC ) of 6.62%, 5.45%, 2.13%, 3.36%, 4.09% and 3.60% respectively ( P <0.05). Conclusion Internet addiction among adolescents in Shanghai showed an increasing trend in some groups from 2004-2019, but without significant differences by year in the overall groups. Comprehensive prevention and control programs are needed for adolescent Internet addiction, especially for those with mental health problems.