In order to improve the fault-tolerance of wide area backup protection and make it has satisfactory performance in complexity operating condition, a wide area protection algorithm combining fault voltage comparison and wide area protection information is proposed. Protection information of the line and the adjacent line are weighed to get the comprehensive value, then the corresponding probability of failure is calculated by the ratio of comprehensive and threshold value. At the same time, measured voltage and current by phasor measurement unit (PMU) from one terminal of transmission line are provided to estimate the voltage fault components of the other terminal. Then the corresponding probability of failure is obtained by the ratio of measured and estimated value, these two probabilities are weighted comprehensive to find the fault component. The principle of this algorithm is simple. The simulation tests based on IEEE 5-generator 8-bus system illustrate the validity under various complex conditions, such as high impedance earth fault, open-phase running of fault again, fault conversion, etc. And it shows the effectiveness and high fault-tolerance capability of the algorithm with the mis-operation and refuse-operation of multiple protections.