Step approximation of refractive index has been adopted to discrete the grad'ed-index layer of GRINSOH-SQW iaser into many sublayers to obtain the eigenvalue equation of the waveguide. The effective refractive index of the fundamental mode has been calculated by using numerical method to solve the eigenvalue equation. By calculating the near-field optical intensity distribution in the direction perpendicular to the junction plane, we have calculated the optical confinement faotorr which is closely rlated to the threshold current density. Based on this, influence of the waveguide parameters on the optical confinement properties has been discussed.