The uncertainty of ozone differential absorption lidar (DIAL) measurements due to the effect of background noise is presented. The effect of background noise on ozone concentration profiles is proportional to the background intensity and the ratio of return signal intensities at “on” and “off” wavelength. Analysis suggests that an appropriate return signal intensity ratio can make the effect of background signal very small, negligible. The simulations based on the analysis coincide with the experimental results.The experimental results show that the impact of background signal is negligible at an appropriate return signal intensity ratio of 0.96 at wavelength pair (280 nm,285 nm). In case of unknown background intensity, we can adjust the laser pulse energy levels at the two wavelengths to obtain an appropriate return signal intensity ratio on the oscilloscope to suppress the impact of background signal and ensure the accuracy of night time ozone measurements.