Objective To investigate the status quo of smoking in junior middle school students in Jiading District of Shanghai and its influential factors, so as to formulate targeted interventions. Methods The investigation of smoking among junior middle school students, grade first to grade third from 8 of 24 schools in Jiading District of Shanghai, was done by the online anonymous self-administered questionnaire using the stratified cluster random sampling method in October 2017. Results Junior middle school students trying smoking rate was 4.95% in Jiading District. It was lower than the adolescents trying smoking rate on the average in our country. The effects of sex, school, friends of the students and their family members living together whether there are smokers, sources of influence, self-awareness of tobacco use, and other factors on smoking behavior were statistically significant. Conclusion Adolescents trying smoking is affected by individuals, peers, families, schools, social environment and other factors in Jiading District of Shanghai. These should be the focus of measures to prevent junior high school students from becoming smokers.