A new method to measure real-time sensitivity of Doppler lidar is presented, to solve the sensitivity uncertainty problem caused by the spatial and temporal change of aerosol during wind detecting. Two receive channels of rotational Raman spectrum are added, system receives elastic scattering spectrum and rotational Raman spectrum respectively with beam splitters and interference filter so as to acquire the aerosol backscattering ratio for sensitivity calculation. The two rotational Raman spectrums, central wavelength of 531.3 nm and 528.7 nm, are detected with 532.25 nm wavelength single longitudinal mode laser. Data simulation and analysis show that the system is capable of measuring aerosol backscattering ratio profile of low-altitude troposphere (within 5～8 km) under conditions of laser energy of 300 mJ, 270 mm diameter telescope, and the on-line calibration can improve the accuracy of wind measurement.