This paper studies the effect of aerosol on the three-wavelength dual differential absorption lidar(Dual-DIAL)method with the presence of aerosols in Nanjing, the wavelength pair 266 nm,289 nm,308nm is used for errors analysis; based on the error analysis of the actual aerosol, the best value of C which minimizethe error isobtained as 1.7 ,and have been compared with thevalue derived by the traditional method; the influence of aerosol distribution and loading on the Care discussed , the variation of the errors with aerosol under different C is discussed, too. As the paper shows, 1.7 and 23/19 are two suitable values of C, since the aerosol distribution homogeneously, C=1.7 enable the error under 5% , but increases soon when the aerosol change frequently, maximally reach to 40%;the errorscan be stable when 23/19 as a value of C, errorsarenot greater than 10%, and the errors decreases with the height ;the value of C at different aerosol distribution is discussed.