The invention discloses a wideband low-distortion combined three-phase inverter which solves the problems that an existing three-phase inverter cannot perform inversion in a wide frequency range, the waveform distortion degree of output voltages is high, the unbalanced load capacity of a system is low, and the adjusting accuracy of output frequency is low. The wideband low-distortion combined three-phase inverter which performs variable frequency regulation in a wide frequency band range comprises an inversion power source control portion, a comprehensive control portion and a main control portion. The inversion power source control portion comprises a power input circuit, a three-phase rectifying circuit, a three-phase inversion circuit, a high-frequency transformer, a high-frequency inversion power source, a high-frequency rectification filter circuit, a power output circuit, a voltage/current sampling circuit and a digital signal processor. A self-adaptive synchronous modulation method and the polarity frequency multiplication modulation and embedded compound control (repetitive control and PID control) combined control strategy are adopted in the wideband low-distortion combined three-phase inverter. The wideband low-distortion combined three-phase inverter belongs to the scope of special power sources and can be applied to the fields of fault diagnosis, fault analytical tests and the like.