The Available Transfer Capability (ATC) is an important metric of the power system. With the development of AC/DC hybrid system, the research on the ATC of the AC/DC hybrid system attracts more and more attention. However, the large scale property of the power system makes it hard to calculate the ATC in real time. In this paper, it is presented a novel fault ranking algorithm for ATC calculation in AC/DC hybrid systems. Both the probability of occurring a certain fault and its impact on the power system are considered in design. Through the proposed method, the faults are ranked according to their consequence function, and the critical faults are selected to construct the fault set and calculate the ATC of the AC/DC hybrid system. An extensive simulation is conducted based on a modified IEEE 30-bus system to examine the effectiveness of our design. The results indicate that the proposed method can reduce the running time of ATC calculation without decreasing the precision. The calculation efficiency can be increased through this method.