Combined with the assumption of normal stress distribution on sliding surface and the spatial analysis capability of Geographic Information Systems（GIS）

a three-dimensional（3 D） slope equilibrium model based on grid cells is established

and a GIS-based slope stability calculation method is proposed. In this method

a 3 D slope stability analysis model based on grid cylinder elements is firstly established

and the spatial computational expression of each parameter in GIS is clearly articulated. Secondly

under the condition of limit equilibrium

a set of stability analysis equations

including three force equilibrium equations and one moment equilibrium equation of the sliding body

are derived for solving the three-dimensional safety factor. Finally

following the Mohr-Coulomb strength criterion and the assumption of normal stress distribution on the sliding surface

the three-dimensional safety factor is solved. Moreover

the component object model（COM） technology is used to develop a GIS-based 3 D slope stability analysis module

which can be implemented for the complex algorithms and the calculation of multiple stratigraphic slopes and multiple combinations of factors in 3 D slope stability analyses. The correctness and feasibility of the module are verified by three typical cases.