The invention discloses a fault detection device for an inverter machine. The fault detection device comprises a center processing unit, a voltage-adjustable power source, multiple voltage and current sampling circuits, an IGBT signal generation circuit, a load selection circuit, a load resistor and a direct current power load. The fault detection device applies an electrical condition similar to the working state to the to-be-detected inverter welding machine; then the multiple sampling circuits are used for measuring the voltage and current values of the inverter welding machine; the center processing unit compares the various voltage values and current values obtained through measurement with preset values or preset ranges; the specific fault types of the welding machine are obtained through comparison results; and fault reasons of the welding machine are displayed through a touch screen, and corresponding maintenance suggestions are given. The maintenance process of the inverter welding machine is greatly simplified, and the requirement for the professional skill of maintenance personnel is lowered.