The wire used for car suspension spring has strict requirements on steel purity, dimensional accuracy and surface quality. It has been proved that the diameter accuracy of wire rod is of great significance to reduce the wear of drawing die, reduce energy consumption, reduce wire breakage and ensure the stability of drawing. Suspension spring wire diameter tolerance control in ±0.2mm, ellipticity is not greater than 60% of the diameter tolerance. The defects of wire surface such as crack, fold and scratch seriously affect the quality of wire and reduce the fatigue life of suspension spring. Wire surface should be smooth, must not have crack, fold, scar, ear. The size of local bumps, pits, pockmarks and other defects shall not be greater than 0.10mm. Wire mechanical property is good, and fluctuation is small. The fluctuation of tensile strength of wire rod is ≤40MPa, the fluctuation of section shrinkage is ≤15%, and the volume fraction of sortenite is ≥85%. The free ferrite has great influence on fatigue life, and the volume fraction should be controlled within 1.5%, the grain size should be above grade 8, and no martensite should be allowed.