This paper proposes an improved droop control strategy, in view of the problems brought by conventional droop control for microgrid inverters, like as the fluctuation of the voltage and frequency in the island mode and being susceptible when the main grid suffers any disturbance in the grid-connected mode. The principle is an introduction of feed-forward bias currents based on conventional droop control, which speed up the response of the system and can make inverters work as grid supporting sources in the grid-connected mode, when the main grid voltage suffers any variation, the inverters will respond with variation of active power and reactive power, so that restore the main grid voltage and frequency and increase the stability of the whole system. In the island mode, the proposed control method can accurate the value of droop characteristic dynamically, broaden the range of power adjustment, and meet the requirement of power balance. At last, simulate and analyze the two typical running mode of microgrid and transient process of mode switch with simulation software PSCAD/EMTDC, verify the effectiveness and reasonableness of the proposed control strategy.