Due to its characteristics like the variation of the operation mode and the difference with traditional power grid on network topology structure, micro grid needs to be provided a new protection principle. To a tee, the real-time characteristic of adaptive current protection is consistent with the problem. This paper firstly proves that the existing adaptive protection principle applying to those micro grid which may arise two-way short circuit current in the same line when a fault occurred was prone to error, and carries on a principle to be more perfect. Then, a new algorithm of adaptive current protection is tried the —— key parameter (the equivalent impedance) is calculated by using the intersection point of three impedance circle, added with the adaptive mutation algorithm, to avoid the problem that the original algorithm is prone to be disturbed. Afterwards, through the PSCAD model simulation of typical micro grid, the results validate that the protection has the ability to correct the mistakes of the original principle using in certain situations, and demonstrate its better stability and accuracy than the original algorithm. This work is supported by National Natural Science Foundation of China (No. 51477090).