This paper presents the numerical calculation on the performance of Savonius-type vertical axis wind turbine (VAWT) with changing various twist angles and aspect ratios. A series of numerical simulation has been made to predict the power and torque of the VAWT with the aiming to apply for the future application in the real site. For the numerical simulation of VAWT, The unsteady RANS(Reynolds-Averaged Navier-Stokes) equation is applied for analyzing the highly turbulent flow with RNG k-? turbulence model. As one of key parameters in the VAWT design, the twist angles and aspect ratios were chosen. the range of twist angles are 0° , 45° 90° , 135° , aspect ratios of rotor height(H) and diameter(D) are 1:1, 1.33:1, 2:1, 4:1. The numerical results include the typical torque and power coefficients against the TSR(Tip Speed Ratio). As a preliminary results, the twist angle of 135° shows the best performance.