Introduction: Functional constipation is a chronic disease that is common in children and adults around the world. The treatments for functional constipation include diet and lifestyle interventions, medications, and surgery. The diet pattern plays an important role in the occurrence of constipation. We found in clinical practice that simple application of drugs cannot achieve long-term relief of constipation, and a large number of patients are not satisfied with the existing treatment. We have concluded that Qingjiang Tiaochang Recipe (QJTCR) and light vegetarian diet (LVD) can effectively improve constipation. However, there is no enough evidence for the description of the effect. This protocol aims at exploratorily investigating effectiveness and safety of LVD and QJTCR following a rigorous clinical trial. Methods and analysis: We will recruit 90 patients to participate in this prospective, placebo-controlled, randomized trial, and exploratory study at the China-Japan Friendship Hospital, including traditional Chinese medicine group, placebo + diet group, traditional Chinese medicine + diet group. Patients in the diet intervention group must strictly abide by LVD, and the study will continue for 28 days. During the intervention period, we need to record a designed diary to assess diet quality and defecation. The primary outcomes for this clinical study were weekly complete spontaneous bowel movements. The secondary outcomes were constipation-related symptom rating scale, traditional Chinese medicine syndrome scale, and 48-hour gastrointestinal transit time, high-resolution anorectal manometry, Bristol stool score, constipation quality of life assessment scale, constipation symptoms self-assessment scale, short-chain fatty acids in feces. In addition, the study will determine the safety of the intervention.