This study investigates the soil-structure interaction of a piled Gravity Base Foundation (piled GBF) supporting an offshore wind turbine tower. The piled GBF is a gravity base foundation supported by five piles with one center and four outer piles. A series of three-dimensional finite element analyses were performed to investigate p-y characteristics in the piled GBF. The results were validated against centrifuge test data prior to undertaking a detailed parametric study, exploring the relevant range of parameters in terms of foundation type, vertical load due to the gravity base self-weight, loading height, undrained shear strength, and the pile bearing condition. Overall, the center pile of the piled GBF showed the highest ultimate soil reaction force, while the leading pile indicated the lowest value. Due to the rotation of mat and self-weight of GBF, significant shear failure was mobilized near the leading pile, which reduced the ultimate soil reaction force. This was also confirmed through the comparison studies with group pile (no mat), piled raft (low self-weight of mat) and rock-socketed piled GBF (no rotation of mat).