In order to achieve high-homogeneity pumping source of semiconductor laser, the influence of microlens changes in the imaging beam integrator on the homogeneity of pumping light is researched. The relation between microlens numerical aperture and the divergence angle of the incident beam is discussed in detail. The far field distribution model of the Gaussian beam passing through the imaging beam integrator is established, in order to analyze the impact of the diffraction of microlens edge on the spot homogeneity. The upper and lower limits of clear aperture of microlens are confirmed to provide a range value for the optical design of the imaging beam integrator. Finally, the software simulation results with ZEMAX and experimental result are compared, showing that the spot of inhomogeneity 8. 11% is achieved by the optimized imaging beam integrator.