Collimation of optical axis is an important issue for biaxial laser ceilometer which will affect the performance of the instrument.By analyzing the influence of axis parallel deviation on the overlap factor,a collimation method for biaxial laser ceilometer based on CCD imaging is put forward.The parallelism of the light axis is adjusted by calculating center point offset distance of the images,while the images of visible target show in the two CCD cameras which are placed in the back of the transmitter and receiver,and the parallelism error is not greater than 16.5 μrad