In this paper, an approach for beam collimation by pupil segmentation is proposed. In this approach, the divergent or  convergent wavefront of the beam to be collimated is divided into a series of subwavefronts by a microlens array, and the  beam collimation is realized by comparing the difference of centroids between the actual spots and the reference ones  under the paraxial approximation. In the experiment, the size of the beam to be collimated is limited by a stop aperture to  satisfy the paraxial approximation. Using the proposed method, a divergent beam is collimated by a doublet with a focal  length of 100 mm under the paraxial approximation. The test results of the collimated beam by a Shack-Hartmann sensor  show that the root mean square of the wavefront of the collimated beam is 0.02 λ, having a good agreement with results  of the proposed method. The experimental results show that the method is simple, low cost and highly accurate.