In this paper, the analysis process of the subnominal operation of the voltage-source parallel resonant class E frequency multiplier with a 50% duty ratio is proposed. The circuit is only satisfied with zero-voltage switching(ZVS) condition. The slope of the transistor voltage at the turning-on instant is not zero. One design freedom is obtained and can make other parameters specification, i.e. maximum transistor voltage. The proposed multiplier is more robust and can operate at a higher frequency. To demonstrate the analysis process, the simulation process is carried out by Pspice. Two subnominal circuits are designed and simulated. The simulated output powers are 14.4 W and 4.3 W, respectively. The simulated results are well agreed with the theoretical.