Abstract: It is important to study the confined groundwater range of action in the translational landslide. It is helpful to accurately evaluate the slope stability, and provides a reasonable guidance for the study on disaster mechanism and disaster prevention of translational landslide. The dip angle of the rock formation is small. The influence of the dip angle is usually neglected in the analysis of the confined groundwater range of action in the translational landslide. Based on the theory of groundwater flow to canals, considering the dip angle, the analysis model of groundwater seepage about the translational landslide is established. A new formula calculating the confined water range of action is deduced. The sensitivity of confined groundwater to the dip angle is analyzed in detail. The concept of the sensitive dip angle is put forward. The calculation results show that the dip angle has significant effect on the confined groundwater range of action. This effect is closely related to the thickness of the permeable layer, the seepage discharge, and the coefficient of permeability. The greater the thickness of the permeable layer, the more significant the dip angle impact on the range of action of confined groundwater. Meanwhile, the sensitive dip angle is influenced by the thickness of the permeable layer, the seepage discharge, the coefficient of permeability and so on. At last, the new model is used to analyze the landslide. The rationality of this new model is verified.