Every year many watershed hillslopes are displaced by landslides resulting from deforestation or rainfall-induced saturation. This destruction can lead to extensive loss of life and property damage if it occurs in the vicinity of roads or buildings. The intensity of landslides depends on the degree of saturation influenced by infiltration, hillslope geometry, and soil characteristics. This research's main purpose is to investigate the effect of two features of geometry, the plan shape (convergence and divergence) and profile curvature (convexity and concavity) on the stability of complex hillslopes. TOPMODEL is a hydrological subsurface flow model that can predict the magnitude of saturation and soil moisture deficit at any watershed point. In this research, TOPMODEL equations were developed so that the geometry of hillslopes could be considered. The saturation index in TOPMODEL was linked to SINMAP slope stability model to estimate the stability of different points of the complex hillslope. It was concluded that convex hillslopes are more stable than concave ones. Moreover, divergent hillslopes showed less sensitivity to land sliding compared to convergent ones. All in all the minimum stability was corresponding to the divergent convex hillslope. Finally, the effect of some other geometric parameters (e.g. slope angle, profile curvature parameter, and plan shape) on the stability of hillslopes was examined.