DPB for video coding system; a method and apparatus for managing (decoded picture buffer the decoded picture buffer) is disclosed. IntraBC mode is assigned based on whether the current is determined whether or not being used in the picture, using the maximum number of allowed IntraBC mode of decoded picture for the current picture in the DPB. Then, the current picture is encoded or decoded by using the decoded pictures stored in the DPB as the reference data. In another method, the maximum number of the pictures reordered in DPB is determined. If certain conditions are true, the one or more decoded pictures stored in the DPB will be evacuated until it is not true any of the conditions also. One condition corresponds to the case where the number of decoded pictures in the DPB marked as "required for the output" is greater than the maximum number of modified reordering pictures in accordance with whether or not a current picture using the IntraBC mode.