A wireless power transfer (WPT) system usually needs dual-side cooperated control for efficiency optimization and power regulation, and requires wireless communication between the transmitter and the receiver. Phase shift keying (PSK) communication is a good choice for WPT systems because of its advantages of high security and low hardware cost. However, the converter phase modulation required by the PSK communication causes output power and voltage fluctuations. In this brief, we analyze the relationship between the phase modulation depth and the output fluctuation amplitude. Then we propose a pulse density modulation-based feedforward power compensation method to compensate the fluctuations caused by the PSK communication. Experimental results show that the proposed power compensator can suppress the output voltage fluctuations to an insignificant level without a large output filter capacitor. The proposed method overcomes the main drawback of the PSK communication in WPT systems.