The present disclosure is related to systems and methods for motion signal recalibration. The method includes obtaining a motion signal of a subject based on positron emission tomography (PET) data of the subject. The motion signal may represent a plurality of motion cycles. The method includes determining a distribution of the motion cycles. The distribution of the motion cycles may indicate a probability that each motion cycle of the plurality of motion cycles corresponds to an actual motion cycle. The method includes correcting the motion cycles of the motion signal based on the distribution of the motion cycles to obtain corrected motion cycles. The method includes reconstructing a PET image by gating the PET data based on the corrected motion cycles.