With the continuous development of laser technology, optical micro-resonator with high Q-value attracts more and more attentions. Apart from broad applications in traditional optics, it also has a considerable prospect in quantum information and quantum integrated chips. Two kinds of micro-resonators are introduced, which are whispering gallery mode and photonic crystal optical micro-resonators. Their principle, history and advantages compared with traditional optical cavity are analyzed in detail. Meanwhile, the mode distribution of different structures of optical micro-resonators are simulated. Based on the unique advantages, the applications of whispering gallery mode optical micro-resonators are introduced in the area of laser, biological detection and quantum physics. And the considerable prospect of photonic crystal optical micro-resonators is predicted in the area of integrated optics and microelectronic technology.