Abstract: Sulfur-based free-cutting steel is the most widely used free-cutting steel. Its surface quality can directly affect the quality of the final production and processing products. It is very important to reduce the defect rate of free-cutting steel billets and rolled materials. 1215MS free-cutting steel was taken as an example, and various quality defects were studied by metallographic microscope, scanning electron microscope and energy dispersive spectrometer. The causes of defects were analyzed and corresponding solutions were proposed. The results show that the common defects in the casting billet are surface longitudinal cracks, subsurface bubbles, chatter mark, etc. The common defects in the rod coil are split head cracking, rolling folding, scarring, pitting and corrosion, etc. The common defects in drawing are cracking, skin peeling and material loss, etc. The special chemical composition characteristics of the sulfur-based free-cutting steel and some operations in the production process are the main causes of defects. In view of the different defects and their causes, the final quality of the product can be improved by optimizing the production process, improving the quality of the mold powder and improving the product transportation method.