Abstract: To characterize precisely the usage of visibility to retrieve concentration of fine particles, a direct method and an indirect method were used to reckon PM_2.5 mass concentration based on visibility in a comparative study with the hourly monitoring data of PM_2.5 mass concentration and atmospheric visibility at Section 4 of South People Road of Chengdu during the period from June 1, 2013 to Feb. 28, 2014 cited as subject. The former used power functions to directly develop a functional relationship between visibility and PM_2.5 mass concentration, while the latter first worked out extinction coefficient by visibility and then used linear functions to retrieve PM_2.5 mass concentration. Results show as follows:(1) Both methods can be used well to retrieve PM_2.5 mass concentration and the retrieval matches the ground monitoring data quite well in statistic feature; (2) Compared to the direct method of using visibility to retrieve PM_2.5 mass concentration, the indirect method is more explicit in physical significance and more accurate.