Abstract: Based on the development of microwave photonics, optoelectronic oscillator is a ring oscillator with both optical and electrical paths and converts light energy to microwave signal, overcoming the limitation of traditional microwave oscillator in phase noise performance. With the ability of generating low phase noise high frequency signals in both electrical and optical domain, optoelectronic oscillators are becoming a new kind of high quality microwave signal source. The Oscillation frequency can be tunable, and can cover from several gigahertz to hundreds of gigahertz with Q-factor up to 1010 . The optoelectronic oscillators have received considerable attentions due to their potential significance in applications. In this paper, the current situation of optoelectronic oscillators is investigated, and the phase noise, side mode suppression, frequency stability, frequency tunablility, high frequency output, and integration are discussed.