To achieve more output power of the free-standing magnetic field energy harvester (FSMFEH) with a smaller core volume, designing the core and coil parameters of FSMFEH is critical. However, the lack of an FSMFEH power model leads to the absence of a detailed design method. To address this issue, building an accurate FSMFEH output power model is required. In this article, by quantifying coil mutual inductance and internal resistance as core and coil parameters, an accurate power model of FSMFEH with all parameters is established based on the H-shaped core. As a result, based on the proposed model, the optimal values of the core column size, the core lamination size, the coil turns, and the wire diameter are designed. Experiment results show that the proposed model can maintain high accuracy, and the power density deviation is within 5% compared with the theoretical value. Besides, the optimized parameters designed according to the model analysis are effective for improving the power density. When the current of the busbar is 100 A, the maximum power density can reach 4.182 mW/cm 3 , and the corresponding maximum output power is 13.25 mW with the optimized parameters.