In order to overcome the influence of background light,a side-scatter ing lidar for all-day PM2.5concentration measurement was designed by adding lo u vers.By using all-day lidar equipment,the fitting model between measured PM2. 5concentration and real PM2.5concentration was obtained.The comprehensive devi ation rate,correlation coefficient and fitting degree of the relationship were further analyzed.The analysis results show that compared with the non-louvered lidar,the all-day lidar can not only measure PM2.5concentration at night effe c tively,but also ensure the accuracy of PM2.5concentration measurement during t he daytime.