Microwave photonics is an interdisciplinary subject of microwave engineering and photonics technology. It is a fused microwave and optical system that studies the interaction between optical and microwave signals in the medium and the generation, processing, transmission, and receiving of microwave signals in the optical domain. Integration is an inevitable trend of microwave photonics since the performances of current discrete devices-based microwave photonic systems are poor in terms of size, power consumption, stability and cost. The main scientific and technical issues of integrated microwave photonics were discussed, its development status and frontier research progresses were summarized, and an outlook of its future prospects was given.