BACKGROUND: Chronic lower extremity ulcers are a public health problem that seriously endangers human health. Western medical treatment mostly focuses on anti-infection, circulation improvement, surgical debridement and skin grafting, and there are certain therapeutic bottlenecks. Chinese medicine treatment has a long history and good clinical efficacy, and has formed a unique theory of Chinese medicine external treatment and a large number of effective external prescriptions and external treatment techniques. How to further reflect and explore these advantages of TCM in the treatment of chronic lower limb ulcers, and form a safe and effective TCM treatment plan for chronic lower limb ulcers that can be promoted and used, is of great significance. The study of chronic lower limb ulcers is one of the major research topics in the 11th Five-Year Plan of China, which set up a special research project on the characteristic therapies and external treatment techniques of Chinese medicine. Methods and design: A multicenter, large sample epidemiological survey was used to systematically collect data on chronic lower extremity ulcers. A multicenter, large-sample, randomized, parallel-controlled prospective study of this study protocol was conducted using wound healing rate as the primary efficacy evaluation index, wound healing time, wound healing speed, wound decay time, wound decay speed, and quantitative TCM symptoms as secondary efficacy indexes, and blood routine, urine routine, liver function, kidney function, blood mercury, and urine mercury levels as safety indexes. DISCUSSION: This study evaluated the clinical efficacy and safety of external treatment for chronic lower extremity ulcers by removing decay and stasis and tonifying the deficient muscle, formed a standardized protocol for the treatment of chronic lower extremity ulcers by external treatment of Chinese medicine that can be promoted, and established a clinical efficacy evaluation system that reflects the characteristics and advantages of Chinese medicine treatment.