Because of small capacity and low inertia of the inverter based micro-source, loads changing have great impact on the frequency and voltage of islanded micro-grid. A novel frequency control strategy of micro-source based on the secondary frequency regulation of power system is proposed in this paper. Traditional droop control strategy of micro-grid can't guarantee the frequency of micro-grid operate at rated state when loads change. Besides the P-f droop control strategy, the proposed frequency control strategy introduces the proportional-integral (PI) control into control flow. The process is a no-error adjustment, which is similar to the secondary frequency regulation of power system. Additionally in order to overcome the disadvantage of low inertia of micro-source and micro-grid, a first-order inertia link which imitates the motion equation of the rotor of synchronous generator is added to the proposed frequency control strategy. So the stability of frequency of micro-grid is greatly improved. The typical operation states of micro-grid such as loads change, loads shock, the random loads fluctuation in islanded mode and switch of operation modes are simulated based on MATLAB/Simulink. Simulation results verify the correctness and validity of the proposed frequency control