Restaurant food is one of the important sources of sodium intake in China. We aimed to determine whether a restaurant-based comprehensive intervention program may induce lower sodium content in restaurant food. A randomized controlled trial was implemented between 2019 and 2020 in 192 restaurants in China. After baseline assessment, the restaurants were randomly assigned to either an intervention or a control group (1:1). Comprehensive activities designed for intervention restaurants were conducted for one year. The primary outcome was the difference in change of sodium content estimated by the mean values of five best-selling dishes for each restaurant, from baseline to the end of the trial between groups. In total, 66 control restaurants and 80 intervention restaurants completed the follow-up assessment. The average sodium content of dishes at baseline was 540.9 ± 176.8 mg/100 g in control and 551.9 ± 149.0 mg/100 g in intervention restaurants. The mean effect of intervention after adjusting for confounding factors was −43.63 mg/100 g (95% CI: from −92.94 to 5.66, p = 0.08), representing an 8% reduction in sodium content. The restaurant-based intervention led to a modest but not significant reduction in the sodium content of restaurant food. There is great urgency for implementing effective and sustainable salt reduction programs, due to the rapid increase in the consumption of restaurant food in China.