The frequency stability of a microgrid is analyzed， in which the frequency is regulated by different micro sources using P-f & Q-V droop control. A small-signal state-space model is built considering the dynamic characteristics of the controllers， the power measurement and the system circuit. The eigenvalues are calculated at different steady-state operation points using the small-signal state-space model. Then the eigenvalues and the results of the time-domain simulation are used to analyze the frequency stability when the load impedance， the equivalent line impedance and the droop gains change.