Lidar is an important device for detecting atmospheric parameters. In this paper, a single channel F-P etalon is used as a narrow-band filter to lock the transmittance of 355 nm wavelength emitted laser by control the transmittance of seed laser with 1064 nm wavelength. Not only the background noise can be suppressed and the signal-to-noise ratio can be improved, but also the transmittance of the locked target in the etalon can be tracked to achieve higher detection accuracy.During the experiment, transmittance is controlled at target transmittance with 0.01 precision.