Abstract: As it is an important development trend of passive radar by using multiple FM radio signals to improve detection performance, this paper presents a study on the phase compensation methods for high range resolution signal synthesis of multi-frequency passive radar. Firstly multi-FM radio received signal model is introduced and the impact of single-FM radio received signals phase on high range resolution signal synthesis is analyzed; then two phase compensation methods that are used to adaptively adjust the received signals phase are proposed to achieve the best signal synthesis effect. This paper not only elaborates in theory the internal mechanism of the methods, but also verifies multi-FM signal synthesis can distinguish adjacent targets based on the methods through simulation.