Transeverse mode characteristics of Vertical Cavity Surface Emitting Laser (VCSEL) is investigated. Field distribution and carrier profile are solved self consistently by numerical methods. Kink in L-1 curve was found when higher order mode appear. It is assumed that proton is implanted up to upper side of active region. Thermal effects are not considered. Available experimental data is from the laser in which proton is implanted into active region. Simulation result shows discrepancy with experimental data of small diameter laser. Thermal effects and band bending effects may need to be included.