In order to improve the correctness and fault-tolerance of wide-area backup protection， a novel wide-area protection algorithm using traditional protection components and phasor measurement unit（PMU） data is proposed. Firstly， the online obtained protection components are weighed to get the comprehensive judgment value. Then a Gaussian function is used to get the fault probability. At the same time， using the amplitude of positive sequence voltage and phase angle difference of positive-sequence currents within a line， the probability from PMU is also obtained. These two probabilities are weighted comprehensive to find the fault component. The limit digit number of wide-area backup protection is analyzed theoretically. The simulation tests based on IEEE 14-bus system illustrate the effectiveness and high fault-tolerance capability of the algorithm with the mis-operation and refuse-operation of multiple protections， as well as the detection of multiple faults.