To reduce the impact of polarization- induced fading in coherent differential absorption lidar (DIAL),the basic princi ple of polarization diversity technology (PDT) is studied in a coherent lidar syste m.A dual-wavelength switching DIAL system controlled by STM32is performed.Based on the system,many groups of experiments with balanced detection are conducted using PDT and normal heterodyne detection respectively,and the amplit udes of intermediate frequency (IF) are acquired in different concentrations in an optical path of 20m with single freq u ency detection.And the return power of on light and off light could be solved from these amplitudes of IF.By comparing th e differential information of the return signal power with the reference differential value acquired from the HITRAN database,i t is indicated that the minimum concentration the system could detect with PDT is improved by 4times than those without PDT,and thus a variation of 3.5mg/L o f CO_{2concentration} could be identified corresponding to a range of 2km,which could meet the need of climate research with the requirement of verifying the concentration change of better than 1%.The effects of PDT on eliminating polarization-induced fading and improving the resolution of DIAL detection are verified,which is im portant to the research of DIAL.