An independent microgrid control strategy including voltage source inverter (VSI) and synchronous generator(SG) was proposed, and its small signal stability was analyzed. Both VSI interfaces and SG interfaces used droop control strategy, sharing the load power without real-time communication. A small-signal micro-grid model was developed, including a small-signal model of the synchronous generator and its controller, a small-signal model of the inverter-interfaced micro source and its controller, and a small-signal model of the power network and its load. The eigenvalues were calculated when the droop gains change. The root locus of the principal eigenvalues were obtained when the main parameters change. And the participation factor of different state variables to the eigenvalues was investigated by PSCAD time domain simulations. The results show that the frequency stability is improved greatly by the synchronous generator when all micro sources use droop control. PSCAD time domain simulation verified the correctness of the eigenvalue calculation.