Abstract: Multi-phase interleaved converters is widely used in photo voltaic power generation, electric vehicles, fuel cells and other fields, which have advantages including volume reducing, high conversion efficiency, small current ripple, and lower voltage stress on devices comparing to other topologies.When an open-circuit fault occurs in a branch, there will be a serious decline in system performance. In order to identify the circuit fault in time and employ fault-tolerant strategy, this paper presented a fault diagnosis algorithm that can identify multiple simultaneous faults. The algorithm predicts the phase current according to the structural characteristics of the circuit,and then the least squares method was adopted to determine the operating state of each branch based on the input current and the predicted phase current. Simulations and experiment show that the algorithm is simple and robust to noise.