This paper presents an interval observer-based fault detection (IOFD) scheme in UAVs formation system. Firstly, for the formation system in healthy case, the interval observer is constructed based on the known boundary information of the disturbance term and relative output estimation error. Then, the residual errors that can be used for detecting the actuator faults are developed by the output estimation error. Different from the traditional FD schemes, it is not necessary to design the threshold generators in the IOFD scheme. At last, MATLAB proves the correctness and feasibility of the IOFD scheme.