A picture decoding method, comprising: parsing a video bitstream to obtain a reshaping parameter for converting a reconstructed picture into a high dynamic range, HDR, video picture from slice header and a system-layer picture parameter data unit of the video bitstream, and determining a reshaping parameter used for reshaping the reconstructed picture according to the obtained reshaping parameter; and reshaping the reconstructed picture by using the reshaping parameter; wherein the reconstructed picture is a standard dynamic range, SDR, picture obtained by decoding a to-be-processed video bitstream; wherein obtaining the reshaping parameter, and determining the reshaping parameter comprises: obtaining a sixth reshaping parameter from the system-layer picture parameter data unit in a transport stream or a media file for carrying the video bitstream; updating or re-determining the reshaping parameter used for reshaping the reconstructed picture by using the sixth reshaping parameter; wherein the system-layer picture parameter data unit includes description information or auxiliary information corresponding to the AU of the video bitstream; wherein the updating or re-determining the reshaping parameter used for reshaping the reconstructed picture by using the sixth reshaping parameter comprises: determining a picture parameter set, PPS, identifier in the slice header comprised in the AU of the video bitstream; and obtaining the reshaping parameter used for reshaping the reconstructed picture according to the PPS referred to by using the PPS identifier; and updating or re-determining the reshaping parameter used for reshaping the reconstructed picture by using the sixth reshaping parameter. parsing a video bitstream to obtain a reshaping parameter for converting a reconstructed picture into a high dynamic range, HDR, video picture from slice header and a system-layer picture parameter data unit of the video bitstream, and determining a reshaping parameter used for reshaping the reconstructed picture according to the obtained reshaping parameter; and reshaping the reconstructed picture by using the reshaping parameter; wherein the reconstructed picture is a standard dynamic range, SDR, picture obtained by decoding a to-be-processed video bitstream; wherein obtaining the reshaping parameter, and determining the reshaping parameter comprises: obtaining a sixth reshaping parameter from the system-layer picture parameter data unit in a transport stream or a media file for carrying the video bitstream; updating or re-determining the reshaping parameter used for reshaping the reconstructed picture by using the sixth reshaping parameter; obtaining a sixth reshaping parameter from the system-layer picture parameter data unit in a transport stream or a media file for carrying the video bitstream; updating or re-determining the reshaping parameter used for reshaping the reconstructed picture by using the sixth reshaping parameter; wherein the system-layer picture parameter data unit includes description information or auxiliary information corresponding to the AU of the video bitstream; wherein the updating or re-determining the reshaping parameter used for reshaping the reconstructed picture by using the sixth reshaping parameter comprises: determining a picture parameter set, PPS, identifier in the slice header comprised in the AU of the video bitstream; and obtaining the reshaping parameter used for reshaping the reconstructed picture according to the PPS referred to by using the PPS identifier; and determining a picture parameter set, PPS, identifier in the slice header comprised in the AU of the video bitstream; and obtaining the reshaping parameter used for reshaping the reconstructed picture according to the PPS referred to by using the PPS identifier; and updating or re-determining the reshaping parameter used for reshaping the reconstructed picture by using the sixth reshaping parameter.