Abstract: A new leakage protection method was proposed which was based on least-square matrix algorithm. In the method, zero sequence current signal of each brance is extracted on the basis of additional DC source system, and DC component of the zero sequence current signal is extracted by the least-square matrix algorithm. According to the DC component, insulation resistance value of each branch is calculated. If the insulation resistance value of a branch is bigger than action resistance value, the branch is judged as fault branch. The simulation result shows the method is accurate，reliable and with high adaptability.