The invention discloses a preparation process of a round flat steel wire suitable for a valve spring, and belongs to the technical field of heat treatment processing of a metal material. The process comprises the following steps: pickling and phosphating, performing round mold drawing, performing quench tempering, collecting a plate, performing rolling molding, destressing and tempering, and packaging and putting in storage. A round steel wire subjected to pickling and phosphating as well as round mold drawing is subjected to process routes of performing quench tempering treatment, performingrolling molding and then destressing and tempering. By the process provided by the invention, the axial torsion of the similar round flat steel wire in the production process can be effectively controlled, and the similar round flat steel wire for the valve spring can be produced and has the advantages of high precision, uniform stress, convenience in processing, high bearing capacity, excellent fatigue resistance and excellent elasticity attenuation resistance; meanwhile, the preparation process has the advantages of simple process, good steel flatness, high precision, low torsion degree, high spring winding finished product rate and the like.