INTRODUCTION: A number of smartphone apps have been proved to be effective in assisting smoking cessation in many countries, but little is known about the effectiveness of smartphone apps that assist in smoking cessation in China. This study aims to evaluate the efficacy of cognitive behavioural therapy (CBT)-based cigarette smoking cessation smartphone app for treatment-seeking smokers in China. METHODS AND ANALYSIS: In this remote control, randomised controlled trial, the participants will be randomised and allocated in 1:1 ratio to smoking cessation app intervention group or to control group. Participants will receive a 12-week intervention (treatment group will receive CBT-based cigarette smoking cessation smartphone app intervention and control group will receive text messaging-based control intervention) with follow-up at week 26. The primary outcome includes biologically verified continuous smoking abstinence at week 26 after the quit date. The main secondary outcomes include 7-hour point prevalence smoking abstinence at weeks 1, 2, 3, 4, 8, 12, 16, 20 and 26, self-reported continuous smoking abstinence at weeks 4, 8, 12, 16, 20 and 26 after the quit date. About 1200 smokers with willingness to make a quit attempt within a month from January 2021 to August 2021 or until the recruitment process is complete will be recruited. The final 26-week follow-up will be completed in August 2022. The trial results will be available by the end of 2022. All analyses will be done on an intention-to-treat basis. Based on the previous studies, we hypothesised that this CBT-based app will be an effective, feasible and accessible smoking cessation app in China. ETHICS AND DISSEMINATION: Ethical approval was obtained from the ethics committee of Sir Run Run Shaw Hospital, an affiliate of Zhejiang University, Medical College (number: 20200129-33). Study results will be disseminated via research conference presentations and peer-reviewed publications. TRIAL REGISTRATION NUMBER: NCT04421170.