Phosphating is an important process in the pretreatment process for coating to improve the adhesion and corrosion resistance of the coating.The flow of the phosphating solution in the tank will have an impact on the phosphating film.The stirring tubes of the phosphating tank need to be arranged reasonably to eliminate areas with low flow rates in the tank as much as possible.The fluid flow in three phosphating tanks was studied and compared by CFD,so as to design the position of the stirring tube reasonably.