A kind of dual-loop optoelectronic oscillator (OEO) with high stability, high spectral purity and low phase noise is introduced . The principle of OEO is analyzed theoretically. Side-mode suppression is achieved by using dual-loop in optical domain. The length of fiber loop is controlled by detecting the change of output signal′s frequency. Experiment results of a 20 GHz radio frequency signal with high quality are obtained. It has high spectral purity. Its line width is less than 1 Hz and phase noise is -112 dBc/Hz at 10 kHz. And its frequency stability achieves 10-10 in 4 h.