To solve the low transfer efficiency caused by the physical constraints of the receiver in wireless power transfer systems, we establish a model for a non-symmetrical four-coil system based on the circuit theory to derive expressions for system efficiency. Then, we analyze the main parameters that affect the efficiency. The results indicate that the loss efficiency due to a reduction in the size of the receiving coil size can be offset by increasing the size of the transmission coil. Lastly, we establish a finite element model and an experimental device. Our experimental and simulation data are in good agreement with the theoretical data, thereby verifying our theoretical analysis and providing a basis and experimental data for further research of non-symmetrical systems.