Abstract: Recently, the applications of microwave photonic technique in radar system, communication system and electronic warfare have drawn a lot of attention. In this paper, the developments and advantages of microwave photonic technology are introduced firstly. Then, the limiting factors of the engineering application of microwave photonics in radar phased array are demonstrated, such as huge electro-optic and optic-electro conversion loss, low integration, poor channel consistency, high cost, etc. Next, we propose three typical applications of microwave photonics in radar phased array. To overcome the existing limits, some key technologies should be developed including high-efficiency electro-optic/ optic-electro conversion, high-performance microwave photonic links and hybrid-integration. We hope that with the development of these key technologies, the microwave photonics could be widely applied in the radar phased array.