A method and apparatus for IntraBC (Intra-block copy) coding for a coding region are disclosed. The method operates to receive input data associated with a current block in the coding region and determine a maximum memory size of a reconstructed sample memory for storing a constrained previous reconstructed region, wherein the constrained previous reconstructed region comprises a group of previous reconstructed samples processed before the current block. The method then derives an IntraBC predictor from a valid previous reconstructed region within the constrained previous reconstructed region stored in the reconstructed sample memory, and applies IntraBC encoding or decoding to the current block using the IntraBC predictor derived.