The present disclosure provides a method for imaging of moving subjects. The method may include determining a motion range of a region of interest (ROI) of a subject in an axial direction. The method may also include causing a radiation source to emit, at each of a plurality of axial positions relative to the subject, radiation beams to the ROI to generate an image frame of the ROI. The radiation beams corresponding to the plurality of axial positions may jointly cover the motion range of the ROI in the axial direction. The method may further include determining a position of the ROI in the axial direction based on the image frames of the ROI, and determining, based on the positions of the ROI in the axial directions, at least one time bin in which therapeutic beams are to be emitted to the ROI.