On the basis of analyzing the actual engineering data and the limitation of existing instability models, a new conceptual artesian water model of reservoir bank slope is proposed. The conditions pertinent to artesian water model are given. Theoretical calculation formulae for artesian water pressure at the bottom of the sliding zone and for factor of safety of reservoir bank slope are deduced respectively considering the artesian water. It is verified that the existence of artesian water is reasonable. The influence of rainfall infiltration and water level fluctuation on the stability of bank slope is significant by considering the artesian water. The combined effect of these two factors is greater than the simple superimposed effect of single factor respective action. The stability of artesian water slope is the lowest when the infiltration ratio belongs to the range of (10-5, 10-2). The slope is prone to slide when the factor of safety reaches the minimum value. With the same infiltration ratio, the larger the rainfall infiltration is, the lower the landslide stability is.