This paper has attempted to compile the main aerodynamic models that have been used for performance prediction and design of straight-bladed vertical axis wind turbine. Firstly, momentum models (specified as Rotor Blade Model and Streamtube Model) are basically based on calculation of flow velocity through turbine by equating the streamwise aerodynamic force on the blades with the rate of change of momentum of airflow, which is equal to the overall change in velocity times the mass flow rate. And then, according to this theory, Laser Doppler Velocimeter (LDV) was used to investigate two dimensional unsteady flow around Vertical Axis Wind Turbine at three different low tip speed ratios in wind tunnel. In order to clear the characteristics of power coefficient curve, the pressure distribution on the surface of rotor blade were also measured during rotation. Comparing the results, it is concluded that the power coefficient which is calculated from momentum models quantitatively agrees well with the experimental data, except when the blade is at a high tip speed ratio.