Abstract: Coherent ladar adopts laser local oscillator coherent detection and achieves mixing and common mode rejection through balanced photodetectors, which has the advantages of high detection sensitivity and strong anti-interference ability. The advantages and technical charactristics of coherent detection ladar system are presented in this paper, and the synthetic aperture ladar (SAL) and inverse synthetic aperture ladar (ISAL) research progress based on unit-detector / array-detectors are introduced. The issues of coherent ladar waveform and polarization selection, signal processing methods, detection range equation and detection performance under beam-expanded situation, detector form and detection sensitivity are discussed. On this basis, the characteristics of ladar based on diffractive optical system and the demand for laser/ infrared composite imaging detection are further analysed. The application prospects of coherent ladar are also discussed.