The present disclosure relates to systems and methods for energy imaging. The method may include obtaining a reference waveform of a tube voltage of a radiation source of a scanner. The reference waveform may be formed based on a superposition of a sine wave and one or more harmonics corresponding to the sine wave. The method may include causing a high voltage generator to generate the tube voltage changing between a first voltage and a second voltage lower than the first voltage according to the reference waveform. The tube voltage may be provided to the radiation source for generating radiation rays. The method may further include causing the scanner to perform energy imaging.