Abstract: Disclosed are a fault prediction method and apparatus for a power conversion device, and a power conversion system. The method includes: acquiring multiple output voltages of a detecting coil in a preset time period, wherein an electromagnetic induction is generated between the detecting coil and a switching-on circuit of a switching transistor in the power conversion device; extracting each output frequency corresponding to each output voltage of the detecting coil; predicting time when the power conversion device fails according to a change trend of each output frequency. The apparatus includes a detecting coil and a data processing device; the detecting coil is connected to the data processing device and is a closed coil; the data processing device is configured to: acquire an output voltage of the detecting coil, extract corresponding output frequency, and predict time when the power conversion device fails according to a change trend of each output frequency.