Placing multiple wave energy converters (WECs) on a central floating platform has become a popular approach of ocean energy conversion in recent years. The strong interaction between the WECs and the platform brings a number of technical challenges for the design of such devices. The present study investigates the effect of the platform motion on the WEC array of a typical ocean energy harvesting device, consisting of a central support platform and eight point-absorber WECs arranged in a circular array. The numerical studies are performed in four stages based on the potential flow solver ANSYS-AQWA. The power absorption of each WEC in isolation and of eight WECs operating simultaneously is evaluated and compared in the first and second stages respectively, revealing the interaction among the WECs. The effect of a fixed and a floating platform on the power absorption of the WEC array is investigated in the next two stages. The systematic studies demonstrates that the heave motion of the platform improves the power absorption of the WEC array for most wave frequencies tested, due to the increase in the wave-surface elevations around the WECs and the phase differences of the heave motion between the WECs and the platform. The opposite is true for the pitch motion of the platform. Furthermore, the WEC dimension, the platform dimension, and the distance between the WECs and the platform should be optimized based on the actual operating sea conditions to increase the wave-surface elevations and the phase differences. Otherwise, the motion of the platform should be restricted as much as possible.