As the wireless power transmission distance changes, resonance coil offsets, load changes and other aspects of the system's input impedance change, the input impedance will not match with the RF(radio frequency) source impedance, and the transmission efficiency will drop significantly. Adding an impedance matching network between the RF source and the transmit coil can improve the transmission efficiency of the wireless power. In order to improve the accuracy and the speed of impedance matching, an improved particle swarm optimization algorithm was proposed in this paper. By comparing the improved algorithm with the traditional algorithm, it proved the superiority of the improved algorithm in matching precision and speed. Finally, the algorithm was embedded into the automatic impedance matching system and the transmission efficiency of the wireless power transfer system was improved. Meanwhile, the effectiveness of the proposed algorithm was also demonstrated.