The prediction of aerodynamic forces around straight-bladed Vertical Axis Wind Turbines (VAWT) is important for wind turbine applications. This paper focused on evaluating the aerodynamic forces acting on a single blade, depending on the different numbers of blades in wind tunnel experiments. In this study, numbers of blades were from two to five and the cross-sectional shape of the tested airfoil was a NACA0021. Firstly, the power coefficient was measured by a torque meter and a six-component balance. Secondly, pressures acting on the surface of rotor blades were measured during rotation by multiport pressure devices. Then, the evolutions of normal coefficient, tangential coefficient and lift-to-drag ratio C-L/C-D, which were obtained from pressure distributions, were discussed. Finally, the power coefficients calculated by pressure distributions were compared with the experiment data of the torque meter and the six:component balance. The results showed that the pressure difference substantially decreased with the increase of solidity. In addition, the values of six-component balance and torque meter showed smaller values than those calculated by pressure distributions. In words, these results provided theoretical significance towards the development of a simple design for straight-bladed VAWT. (C) 2016 Elsevier Ltd. All rights reserved.