Wind energy has attracted worldwide attention as a pollution-free and widely distributed renewable energy source. Increasing the power density by optimizing the arrangement of wind turbines has been a popular field of research in recent years. In the present work, a systematic study on the influence of array configuration on vertical axis wind turbines is made through wind tunnel experiments. Firstly, the power performance of an isolated vertical axis wind turbine at different tip speed ratios is tested as a benchmark of comparison. Multiple situations of two-turbine configurations are then tested and the results are compared with the isolated wind turbine. The power coefficient of the turbine pair increases by 34% when the turbines are 2.4 rotor diameters apart and rotate in the same direction. In the counter-rotating co-leeward case, it is demonstrated that the turbine pairs will have a positive effect on each other when they are separated by 2.1 rotor diameters to 2.4 rotor diameters. The lateral spacing between the counter-rotating co-windward turbine pair should be greater than 1.5 rotor diameters to avoid turbulence interference between the rotors.