The present invention relates to a thermoplastic resin composition and a preparation method of the same, and more precisely a thermoplastic resin having excellent impact strength, surface gloss, and beautiful color, as well as a high level of hardness and scratch resistance, which comprises a) a primary graft copolymer prepared by polymerization of conjugated diene rubber latex with (metha)acrylic acid alkyl ester compound, aromatic vinyl compound and vinyl cyan compound; and b) a secondary copolymer prepared by polymerization of (metha)acrylic acid alkyl ester compound with aromatic vinyl compound and vinyl cyan compound.