Abstract: Due to the fact that the surface crack plays a major adversary role to affect the quality of steel with ratio being more than 80%, the crack defect becomes the key problem restricting steel product quality. The magnetic flux leakage testing can achieve 100% detection of steel bar, and can to the greatest degree eliminate the differences of testing results for sampled round steel and the actual round steel, thus greatly reducing the cost of technology. Because the magnetic flux leakage testing process can be under monitoring, the detection results can be statistically analyzed and product quality is of traceability, so the product defects can be timely found out, leading to the rapid improvement of upstream production state and playing critical role in preventing quality-related accidents.