A nonlinear theoretical model of the combined Richtmyer-Meshkov and Kelvin-Helmholtz instability between two different density fluids with surface tension is proposed. The model is based on the extended Layzer's potential flow model. It is observed that, the surface tension decreases the velocity but does not affect the curvature of the bubble tip, provided surface tension is greater than a critical value. Under a certain condition it is also observed that surface tension stabilized the motion with nonlinear oscillations. The nonlinear oscillations depend on surface tension and relative velocity shear of two fluids. All results are obtained theoretically and supported by numerical technique.