An apparatus for constituent code processing in polar successive cancellation list (SCL) decoding and a method thereof. The apparatus includes a processor configured to determine an activation value I and a number r of the candidate paths, where I is a binary value and r is an integer, (I, r)=ƒ(R, k, m), ƒ is a function, R is a number indicating node reliability, k is an integer indicating a number of information nodes, and m is an integer indicating a number of leaf nodes; determine min1, min2, . . . , minq, wherein q is a number of least reliable bits; determine r candidate paths; determine path metrics PMtj of a codeword j for each candidate path t; and select r most probable paths based on PMtj.