This study aimed to evaluate the clinical efficacy of Longyizhengqi granule, a traditional Chinese medicine, in patients with mild COVID-19. We conducted a prospective study including mild COVID-19 participants conducted at Mobile Cabin Hospital in Shanghai, China. Participants were assigned to receive Longyizhengqi granule or conventional treatment. The primary outcome was the time for nucleic acid to turn negative and the secondary outcomes are hospital stay and changes in cycle threshold (Ct) values for N gene and Orf gene. Multilevel random-intercept model was performed to analyze the effects of treatment. A total of 3243 patients were included in this study (Longyizhengqi granule 667 patients; conventional treatment 2576 patients). Age (43.5 vs 42.1, p<0.01) and vaccination doses (not vaccinated: 15.8% vs 21.7%, 1 dose: 3.5% vs 2.9%, 2 doses: 27.9% vs 25.6%, 3 doses: 52.8% vs 49.8%. p<0.01) show statistical difference between Conventional treatment group and LYZQ granules group. The use of Longyizhengqi granule could significantly reduce the time for nucleic acid to turn negative (14.2 days vs 10.7 days, p<0.01), shorten hospital stay (12.5 days vs 9.9 days, p<0.01), and increase the changes in Ct value for N gene (8.44 vs 10.33, p<0.01) and Orf gene (7.31 vs 8.44, p<0.01) to approximately 1.5. Moreover, the difference in the changes of Ct values on the 4th, 6th, 8th, and 10th days seem to increase between two groups. No serious adverse events were reported. Longyizhengqi granule might be a promising drug for the treatment of mild COVID-19, and it might be beneficial to effectively shorten the negative transition time of nucleic acid, the total days of hospitalization, and increase the changes of Ct values. Long-term randomized controlled trials with follow-up evaluations are required to confirm its long-term efficacy.