The present invention discloses a method for removing impurities in crude heparin sodium by using a ceramic membrane. According to the method, a dynamic cross-flow filtration manner is adopted. Enzymatic hydrolysate flows on a surface of an inside membrane of a ceramic membrane tube at a certain high flow velocity. The enzymatic hydrolysate flows through a microporous membrane along a direction perpendicular to the ceramic membrane. Macromolecule proteins are retained by the membrane, so that the enzymatic hydrolysate is separated from impurities and purified. The method of the present invention has high separating precision and high filtrating efficiency with the advantages of clear enzymatic hydrolysate, lower impurity content, free of heparin loss, convenient later adsorption, and the like. A product yield can reach 99.5%. Production costs are reasonable. Therefore, the method is suitable for large-scale industrial production.