Rockfalls are the most frequent major hazards in mountainous areas. For both hazard assessment and the design of countermeasures, realistic and accurate prediction of rockfalls is a major need. Thus, a modelling technique for the representation of geographical topography of slope, and shape of rock mass are required. This paper, suggests the application of polyhedron block for rock mass rather than commonly used particles. In this paper, firstly a 3D DDA program has been developed; and then a special element named Contact Face Element has been introduced into 3D DDA for effectively modelling with GIS support. The implement of Contact Face Element also improves the efficiency of both contact searching and solution process. An application of the modelling technique has been provided. It has been shown that the newly developed 3D DDA program is applicable to investigating the 3D shape effect of falling rock blocks and 3D topography effect of the slope.