Abstract: Wireless power transfer (WPT) technology realizes wireless power transfer with aid of high frequency magnetic field. In the multiple pickup WPT system, it is relatively difficult to realize output synthesis control due to unbalance output power capacity for each pickup. Aiming at the stabilizing output voltage for WPT system, this paper proposes a novel output control method for multi-pickup system by using knapsack optimization algorithm. The fundamental principle of multi-pickup system is first analyzed and the relationship between the output voltage and duty ratio of controller is derived. And then, the output voltage control strategy is proposed by using knapsack optimization algorithm. Experimental results verify that this control method can realize fast regulation and stabilize output control for multiple pickup WPT system.