Abstract: Based on high-performance signal synchronization among multiple radars, distributed coherent radar can realize signallevel coherent fusion, significantly enhancing radar detection, tracking, and anti-jamming capabilities, which represents one of the important development directions in the field of radar. As the frequency range and instantaneous bandwidth continue to expand,and platform forms diversify, distributed coherent radar technology demands increasingly precise signal synchronization in terms of time, space, frequency, and phase. This poses significant challenges to traditional electrical signal synchronization technologies.The performance requirements of signal synchronization technologies and reviews of the research progresses are presented in this paper.Then, the basic principles and representative achievements of microwave photonic synchronization technologies which address synchronization challenges in time, space, frequency, and phase domains are summarized. Finally, a proof-of-concept system for microwave photonic distributed coherent detection is constructed, verifying the feasibility of distributed coherent detection. Microwave photonic signal synchronization provides an important technological pathway for advancing the frontier development and engineering applications of distributed coherent radar.