Aiming at the inaccuracy caused by power shortage method using frequency change rate and equivalent moment of inertia,the paper proposes an improved algorithm to enhance accuracy of the power shortage of microgrid. To begin with,the load capacity to be curtailed for the first time is calculated according to the frequency change rate and the approximate equivalent moment of inertia of microgird. And then,the second load curtailment is conducted in line with the frequency change information from the microgrid after the first time. As a result,safe and stable microgrid operation can be achieved by two times of load curtailment. Simulation results show that the improved algorithm can calculate the power shortage without depending on the accurate parameters of equivalent moment of inertia of microgrid,and that it is more superior,accurate and rapid.