Introduction Salt intake in China is high, and most of it comes from that added by consumers. Nevertheless, recent years have seen a rapid increase in the frequency at which people eat out. The aim of this study is to evaluate the effectiveness of interventions designed for salt reduction in restaurants through a randomised controlled trial in China.Methods and analysis As a randomised controlled trial with restaurants as study subjects, we recruited 192 restaurants from 12 counties of 6 provinces in China. After the baseline survey, restaurants were randomly assigned to intervention or control group. Using social cognitive theory, comprehensive intervention activities were designed to encourage salt reduction in all restaurant foods, and at the same time, to encourage consumers to choose lower salt options when eating out. The interventions will be conducted only in restaurants of the intervention group during the first year. The follow-up assessment will be conducted at the end of the trial. The primary outcome is the change in the average salt content of the five best-selling dishes of the restaurant, as measured by laboratory tests. Secondary outcomes include differences in the monthly use of salt and salty condiments between intervention and control restaurants, and the knowledge, attitude and practice on salt among restaurant consumers.Ethics and dissemination The study was reviewed and approved by the Review Board of the National Institute for Nutrition and Health, Chinese Center for Disease Control and Prevention and Queen Mary Research Ethics Committee. Results will be disseminated through presentations, publications and social media.Trial registration number ChiCTR1800019694; Pre-results.