Aimed at the requirements of the fault detection system for the modern large engine of tank, which worked under strong interference conditions, one online fault detection system based on wavelet analysis was designed. The detection nodes were set in a certain type of the engine, the information was transmitted to the center through the CAN bus. Using CAN bus to transmit information could improve the precision of the measurement and control; the wavelet transform and the pattern recognition technology were used for the fault analysis in the control center, by which the people could locate the fault quickly. The application showed that the system would be better applicable to modern digital chariots of maintenance support, and which was used easily, the fault could be detected quickly and efficiently.