For the voids emerged behind the lining to the handful of pressure hydraulic tunnel, established a model by ABAQUS contains a void at top lining based on the exploration of the cause of cavity. In this paper, the internal force and displacement of lining was analyzed with varying the scope of the void at different internal hydraulic pressure, and evaluated the safety of lining under this condition. The computation shows that (1) cavity behind the lining has a significant impact on the internal force of lining. When the internal hydraulic pressure was not existed, compared with none cavity condition, the axial force of lining may be changed several times. And with this condition, the bending moment of lining increases 5.5 times when the internal hydraulic pressure was 0.5MPa. At the same time, the safety factor of top lining decreased significantly. (2)The safety factor of top lining decreased with the cavity scope and internal hydraulic pressure increased. The reducing amplitude of safety factor was small when cavity scope increased, but it was big when internal hydraulic pressure increased. The safety of lining was sensitive to internal hydraulic pressure changed when top cavity existed.