The purpose of this study is to present the new effective stiffness of special RC shear walls with flanges. ACI 318-99 adapt the different design provisions of effective stiffness between simple walls and walls with flanges. But domestic code makes no distinction between simple and with flanges walls. By the nonlinear analysis, maximum loads and displacement are calculated. Therefore the moment-curvature curve is calcultaed by the P-Δ curve. The stiffness ratios of cracked and uncracked section are calculated by the moment-curvature curves. And the stiffness ratios of simple walls and wall with flange are compared.