In this paper,a direct coupling theoretical model in quasi-three-dimension for the gain-wave guide Vertical-Cavity Surface-Emitting Laser (VCSEL) has been created. With the finite-difference method,self-consistent solutions for the injected current density,carrier concentration,optical field and thermal conduction equations are realized to study the characteristics of electrical,optical and thermal fields distribution in VCSEL. A VCSEL with double oxide-confined regions is introduced. The influences of NDBR layers and double oxide-confined regions on the characteristics of VCSEL are analyzed contrastively.The calculation results show that if N-DBR layers are not considered,there must be some errors to the practical VCSEL. The results also indicate that the structure of double oxide-confined regions in VCSEL has been improved greatly the characteristics of lasers,and it provides a method of reducing threshold current and controlling high-order modes.