The modal threshold gain of cylindrical and oxide-confined vertical-cavity surface-emitting laser (VCSEL) with potential applications in optical communication and optical interconnect,is simulated numerically by using Vectorial Field Model. To weaken the parasitic reflections from the shell(perfectly conducting metal cylinder),more practically,it is considered the shell as non-perfect conducting one,or moreover,it is supposed that the shell is separated from the laser. The threshold gain versus pair number of top Bragg mirror in the two situations is compared with that in the case of perfectly conducting metal cylinder. The result shows that the threshold gain curves are similar for high-order Bessel modes,and they are quite distinct for O-order Bessel modes.