In recent years,the unmanned underwater vehicle(UUV)has been widely used in the exploration and development of seabed resources,marine ecological monitoring,as well as in military fields. The formation control of multi-Uuvs has become the focus of domestic and foreign research. A simplified 3-DOF UUV mathematical model is put forward. Then,through Serret-Frenet equation of planar straight line,the UUV path tracking error model is established based on the idea of virtual guidance. The model of UUV formation control is established based on leader-follower method. By using the method of sliding mode control,the controller of UUV is designed. Finally,the UUVs form a preset formation steadily .