The construction quality of the connection between the inverted arch and the side wall has an important influence on the lining structure and the mechanical state of the surrounding rock.The tunnel model which has a weakening connection between the inverted arch and the side wall is established through the FLAC2Dto analyze the mechanical behavior of the tunnel support structure.The results of the water pressure operating conditions under 0.5MPa of hydraulic tunnel are shown：(1)when the lining is calculated as elastic structure unit，the influence of the connecting weakening between the invert and the side wall on the lining is limited.The effect of the deepening of the weakening is increased，but not significant.(2)when the lining is calculated as elastic-plastic solid unit，the lining edge near surrounding rock within the weakening region appear compressive stress concentration when the weakening degree deepen.(3)Effected by the surrounding rock and internal water pressure，The lining internal force decreases when the internal water pressure increased.