For the 1. 31 μm semiconductor laser working ,the far field divergence Angle is too large and the oxidation of Al component in AlGaInAs/GaAs material system leads to the degradation of device performance. Based on the InGaAsP/InP material structure ,GaAsP material is proposed to be used in the upper and lower waveguide layers of semiconductor laser ,which forms a heterojunction structure with the active region composed of InGaAsP material. Compared with the homogenous junction waveguide layer ,the heterojunction waveguide layer can achieve a larger re- fractive index difference between the active layer and the waveguide layer according to the different refractive index of different materials ,so as to achieve a better waveguide restriction. The In1-x Gax Asy P 1-y material composition in 1. 31 μm laser was calculated theoretically ,and the GaAsy P 1-y material composition and thickness were calculated the- oretically according to the refractive index and lattice constant of the material. The ALDS software is used to conduct simulation and comparative simulation analysis of the two structures ,homogeneous and heterogeneous. Finally ,GaAs0. 145P0. 855 material with a thickness of 100 nm is selected as the waveguide layer and the limiting layer respective- ly ,which effectively reduces the vertical divergence Angle of the far field and improves the circular symmetry of the spatial distribution of the laser beam.