We theorically discussed the relation between the refractive index matching and the residual reflectance of the laser glass and cladding glass. The experimental results show that the better the refractive index matching and the higher product of the absorption coefficient and the cladding glass thickness, the lower the residual reflection, which result in the better restraint of the parasitic oscillation in amplified spontaneons emission（ASE ） and the higher gain from the laser system.