To study the small-signal stability of grid-connected microgrid with inverter-interfaced distributed resources， a complete small-signal dynamic model of the grid-connected microgrid is developed. The model consists of two sub-models: a dynamic sub-model of network and loads， and a dynamic sub-model of inverter adopting power（or voltage） and current double-loop control. Firstly， how the equivalent impedance between the penetrated distribution network and the microgrid impacts on the small-signal stability of the microgrid is studied. It is concluded that large equivalent impedance is harmful to the small-signal stability. Secondly， the real and imaginary parts of dominant eigenvalue are compared when the inverter adopts PQ and PV control strategies respectively. It is found that PV control is a desirable approach than PQ control because PV control can eliminate the potential voltage oscillations. The above conclusions are verified by simulation of PQ and PV control responses to a 15% step change of reference output power of a distributed resource.