Microwave signals with low phase noise are indispensable in wireless communication, radar, time and frequency metrology, and deep astronomy. Photonic microwave signal generation approaches are promising. They can break through the bottleneck of classical microwave signal generation methods in many aspects, such as carrier frequency, tunability, phase noise, integrability, and power consumption. The early systems of photonic microwave signal generation were complex, the lasers and related equipment were bulky, which restricted their application outside of the laboratories. In recent years, optical frequency combs based on microcavities develop rapidly. With the advantages of microcombs such as low loss, small size, and ultrahigh stability, the application of microwave photonics based on microcombs has attracted extensive attention of researchers and the systems of photonic microwave signal generation have been intensively studied. In this paper, we reviewed the topic of low phase noise photonic microwave generation with microcombs and prospected the challenges and development trend in the future application of the systems of photonic microwave signal based on microcombs at the end.