The beam expender of a space-borne laser range finder was an afocal telescope, the alignment requirement of which was rigorous. The alignment accuracy was the key factor of the capability of the laser range finder. The sensitivity of optical element and the compensator were obtained by means of computer aided alignment. High precision coordinate measuring and dual-path centering technology were presented, being aimed at the characteristic of performance parameter determined by distance of elements. Finally the wavefront of the system was tested by the 1 064 nm interferometer, the divergence angle was tested using a pin-hole. The result demonstrates that the RMS of the system is better than 0.225λ and the divergence angle is 0.41 mrad. The results meet the requirement of design.