Abstract: In order to calimate laser beam of laser diodes, the principle of beam collimation was analyzed in the fast and slow axis directions. Based on astigmatic surface microlens, one method was proposed to collimate the laser beam by regarding one laser diode as the collimated unit. The effect of filling factor of laser diode on collimation performance was discussed. As an example of laser diode of 0.5 fill factor, the remaining divergence angle of the fast axis reaches about 0.34 and the remaining divergence angle of the slow axis reaches about 2.69. The results indicate that the microlens can collimate the laser diodes beam with high fill factor and the spot area of the collimated light is very small. The research can provide the new feasible collimation method for high power laser diodes.