Net hydrodynamic uplifting force of reversed tainter value in flat-bottom galleries of high-head lock is studied through unsteady flow tests,main result as follows:1)The net hydrodynamic uplifting force of reversed tainter value is composed of two parts,a part is produced of the corridor current,the other part is produced of the valve shaft current. 2)The net hydrodynamic uplifting force of reversed tainter value resulted from the corridor current has liner relation with square of Froude number of orifice current in every opening. 3)The net hydrodynamic uplifting force of reversed tainter value resulted from the valve shaft current has liner relation with Froude number of valve shaft current in every opening. 4)The formula of net hydrodynamic uplifting force of reversed tainter value in flat-bottom galleries of high-head lock is proposed for the first time,the results calculated is in good agreement with the prototype observation,the proposed formula has a high accuracy.