A method for reconstructing target cardiac images is provided. The method may include: obtaining projection data, the projection data including a plurality of sub-sets of projection data, each sub-set of projection data corresponding to a cardiac motion phase； obtaining a plurality of sampled cardiac motion phases； generating a plurality of cardiac images of the plurality of sampled cardiac motion phases by reconstructing, based on the one or more sub-sets of projection data corresponding to the each sampled cardiac motion phase, one or more cardiac images of the each sampled cardiac motion phase； determining a plurality of cardiac motion parameters corresponding to the plurality of sampled cardiac motion phases based on the plurality of cardiac images； determining a mean phase based on the plurality of cardiac motion parameters corresponding to the plurality of sampled cardiac motion phases； and reconstructing the one or more target cardiac images of the mean phase.
