Abstract: With the rapid development of X-ray detectors,photon counting energy dispersive detectors become more and more popular in X-ray imaging area. Using this kind of detectors,a polychromatic X-ray spctrum can be seperated into different energy regions and the photon number in each energy region can be counted independently,thus attenuation coefficients under different photon energies can be obtained. Multi-energy X-ray imaging technique opens up new perspectives within the fields of X-ray imaging. This paper introduces the latest development of photon counting X-ray detector and its application in medical imaging. Also some advantages of this technique in CT imaging are presented in this paper such as dose reduction,SNR improvement and precision improvement of material discrimination. Recently,a lot of research institutes are dedicated to faster electronic device and readout chip for photon counting detectors. With the rapid development of multi-energy imaging,it will bring a large revolution for X-ray imaging.