Motor is regarded as the heart of industry and electric energy is converted into mechanical energy, thermal energy, and other energy through the motor drivetrains. With the development of the energy internet, how to ensure the safe and reliable operation of the motor drivetrain as a link for energy conversion has attracted the attention of researchers. Compared to traditional vibration monitoring, non-invasive Motor Current Signal Analysis (MCSA) is worth investigating because it does not require redundant sensors. By means of fast Fourier transform (FFT) and other methods, we can extract the characteristic quantities in the motor stator current. Compared with the steady-state conditions, most of the motors work under time-varying loads conditions. Studying the change of characteristic parameters in the stator current of the motor under time-varying loads conditions is also the focus of this paper.