Abstract: Crack defects are commonly found on the steel bar products and caused by many factors.Analysis on the causes of the crack defect of bar products by means of the optical microscopy,scanning electron microscopy(SEM) and energy dispersive spectrum(EDS).It is found out that factors causing crack defects can be divided into four kinds:bar matrix in the presence of a large number of non metallic inclusions,surface decarburization,banded structure and sulfide inclusions.Therefore,the countermeasures have been developed through the optimization of steelmaking,continuous casting,electromagnetic stirring and desulfurization technology,and lead to a great increase in the yield rate of the finished products.