An apparatus and a method for constituent code processing in polar successive cancellation list (SCL) decoding and a method thereof. The apparatus includes a processor configured to determine a number of r candidate paths, wherein r is an integer; determine path metrics PMtj of a codeword j for each candidate path t; and select r most probable paths based on the path metrics PMtj. The method includes determining q indicies min1, min2, . . . , minq of least reliable bits in the constituent code, wherein q is a number; determining a number of r candidate paths, wherein r is an integer; determining path metrics PMtj of a codeword j for each candidate path t; and selecting r most probable paths based on the path metrics PMtj.