In order to meet the requirements of advanced electronic systems such as microwave communication, radar, electronic warfare and navigation, a turnkey coupled optoelectronic microwave oscillator with low phase noise based on Sigma-shaped fiber ring structure is proposed. In this scheme, the Sigma-shaped fiber ring structure is used to eliminate the harmful influence of the polarization-induced fading, and the quality factor of the oscillator is greatly enhanced by the regenerative gain characteristic of the active cavity. As a result, a stable 10GHz signal with low phase noise is generated as soon as the oscillator is powered on. The phase noise at 10kHz offset frequency is about -139.26dBc/Hz.