A carbon fiber precursor composition and a method for preparing carbon fiber precursor are provided. The carbon fiber precursor composition includes 100 parts by weight of acrylonitrile; 1-15 parts by weight of co-monomer; and, 0.1-3 parts by weight of stereoregularity controlling agent. The stereoregularity controlling agent has a structure represented by formula (I), Formula (II), Formula (III), or Formula (IV): wherein R1 and R2 are hydrogen, —OH, —COOH, or —NH2; R3 is C2-8 alkylene, or carbonyl; R4 is hydrogen, or C1-6 alkyl; and, R5 is C3-6 alkylene.