Aimed at the prestressed work gate chamber of a spillway tunnel built on batholith,the paper took finite element computer method and combined finite element analysis software ANSYS to carry out three-dimensional finite element calculation.It studied the stress distribution of gate chamber under two different boundary conditions of bonding and separating of concrete and rock mass,and analyzed the effect on the gate chamber under the condition of separation. Calculation results show that the difference of stress distribution in prestressed work gate chamber are mainly concentrated on upstream face and pressure inlet section of gate chamber under different boundary conditions.The effect of separation on the gate chamber is greater. The result can provide reference for the design and construction of work gate chamber.