In this paper, the superposition and compensation theorems are employed to calculate the electric values under the unsymmetrical open conductor states in the three-phase power systems without modifying the bus admittance or the impedance matrices of the original networks. In cotrast with conventional algorithms, the method proposed here is highly accurate, fast, convenient and flexible. It can be applied to the unsymmetrical open conductor calculations which offered in power systems for its design and operation, to determine the settings of relay and automatic deyices, as well as accident analysis.