In space laser communication terminal with coaxial two pieces of reflective mirror of optical antenna, the highest energy part of the incident Gaussian beam can be obscured by the secondary mirror and its bracket, which leads to the loss of energy. In order to reduce loss of energy and improve the transmitting efficiency of terminal, we use an aspheric homogenizer in beam collimation system. The aspheric homogenizer can convert a Gaussian beam to a flattop beam, reduce the loss of energy led by the obscure of the secondary mirror and its bracket and collimate the beam. In the designed aspheric homogenizer system, incidence diameter d is 3 mm, exit diameter D is 12 mm, wavelength λ is 1550 nm, the glass material is BK7, the light intensity distribution is close to uniform on the output surface, and the divergence angle θ is 1.216 mrad. Finally, the spherical beam expander is contrasted with aspheric homogenizer, and the transmitting efficiency of terminal with aspheric homogenizer can be improved by 11.1% under the same condition.