A common baseline method was proposed to realize angle matching of multi-beams and the parallelism between the emission-receiving system with a complex structure. The emission and the receiving systems were aligned separately. They were fixed according to the baseline. The alignment method of the emission system was studied with a focus on the system with many beams， strict angle error between two beams， high magnification， and strict divergence angle requirements. First， according to the emission-receiving relationship of the structural design， the common baseline， which was the floor of the laser bracket， was built. The floor was the interface of the abutment of the emission and receiving systems. Subsequently， the effect of the expander lens， which could change the laser angle， was analyzed. The laser angle was aligned according to the result of the analysis. The long-focus and large-aperture collimator and the high-accuracy multi-beam-axis calibration system were used to test the direction of the laser and the divergence angle， and they aligned in place such that the angle of the laser beam matched the requirement and the error was less than 1'. Finally， the expander lens was abutted with the laser， according to the influence of the beam expander lens on divergence angle and the beam direction， the distance between the positive and negative lens groups was aligned， and the location of the expander was also aligned such that the divergence and beam angles matched the requirement. The error of the divergence angle is 5 μrad. The error of the angle between two beams is less than 5″. The test results show that the deviation of emissive angles is less than 5″ and the divergence angle is （0.042±0.01） mrad. The beam expansion ratio and final divergence angle matched the requirement. It had the conditions for abutting with the receiving system. The results show that the alignment method of the multi-beam laser emission system is of high precision and effective in practical applications.