The invention discloses a fault diagnosis device and a fault diagnosis method based on a multi-agent system and wavelet analysis. The device comprises a mutual inductor group, a data acquisition module, a control and man-machine interaction module, a multi-agent system module, and a database module. Active electronic voltage and a current transformer are adopted by the mutual inductor group; and the data acquisition module comprises a follower circuit, an amplification circuit, a biasing circuit and an alternate-current/direct-current (A/D) convertor. The control and man-machine interaction module comprises a protocol conversion module, a 485 bus, an Ethernet network cable, and an upper computer. The multi-agent system module comprises a task decomposition agent, a task distribution agent, a diagnosis agent, an assisting agent and a decision-making agent. The running of the device is controlled by a control program, the running state of a primary side of a power grid is displayed in real time, and historical data is called by a database; and the acquired signal is sent to the task decomposition agent, the fault diagnosis result of the decision-making agent is received for alarming, and a user is assisted in making a final decision.