Inductive power transfer (IPT) technology is gaining much popularity for wireless charging applications. In this paper, an approach to design and optimize loosely coupled transformer (LCT) is proposed to meet its strict geometry limitation, while achieving the high conversion efficiency. Different from the traditional design method, the resonant current and voltage stress are considered to increase the system efficiency. Based on Series-Series (S-S) compensation, the parameter range of LCT is determined by analyzing transformer equivalent model of LCT. To match the diameter of the secondary coil smaller than 110 mm and 30 mm air gap, an asymmetric LCT with single-layer primary coil and three-layer secondary coil is designed and optimized based on the proposed design approach. Furthermore, the closed-loop controller with variable frequency control is optimized to realize constant current (CC) charging and constant voltage (CV) charging, and its superior performance is demonstrated by experimental results. A 3 kW wireless charging system is built to demonstrate the validity of the proposed method. Experimental results show that the peak system efficiency from dc power source to battery load is 95.69% at 3 kW output power in the transition of CC mode and CV mode.