The embodiment of the invention provides a power supply switching circuit, an electric power steering system and a new energy automobile. The switching circuit comprises a detection module, a pulse width modulation control module, an isolation type conversion voltage adjusting module and an output module. The detection module is used for detecting power supplying states of a power supply for providing power for load currently. The pulse width modulation control module is used for outputting a pulse width modulation signal when the detection module detects that the power supply for providing power for load currently is in an abnormal power supplying state. The isolation type conversion voltage adjusting module is used for adjusting the voltage of another power supply to the load suitable for the load when receiving the pulse width modulation signal output by the pulse width modulation control module. The output module is used for outputting the voltage suitable for the load. A to-be-switched power supply can be any power supply and is free from effects of the grade of the voltage of the power supply. In addition, the voltage adjusting module can be controlled to output the requiredprecise voltage through the pulse width modulation signal. The application range is wide and the cost is low.