To maintain high efficiency over a wide range of load, inductive power transfer (IPT) converter should have the ability of load impedance matching. Recently, a series-series compensated IPT converter with semi-active rectifier has been studied to output a constant voltage, while keep high efficiency by changing the load impedance and the operating frequency. However, the relationships among the power efficiency, output voltage and the load conditions are complicated and not intuitive, and also challenging the design and implementation of this converter. This paper proposes a Particle Swarm Optimization (PSO) algorithm to seek for the optimum modulation for constant voltage and high efficiency over a wide load range. This method is efficient, logical and intuitive, shortening over 95% of the conventional computation time.