Abstarct: Exact understanding of geometry of rock mass is an essential concern in different domains of rock engineering such as maintenance system of underground spaces built in jointed rock masses, designing blasting pattern of rock masses, optimization of fragmentation, determination of cube block in quarry mines and so on. Different kinds of discontinuities turn the rock medium into a collection of rock blocks. The geometry of these blocks, that is, their form and size affect the behavior of the rock mass. Thus, it is necessary to know the volumetric distribution and form of the blocks. The main purpose of this thesis is to study methods of defining geometry of rock mass blocks and choose proper algorithm to develop computer program for this scope and then developing a computer program to determine geometry of rock mass blocks. In this thesis, computer program to determine the geometry of jointed rock mass is written in MATLAB™. The outputs of program according to validation done were corrected. And finally, by using this program some practical examples in aspect of mining engineering such as quarry, blasting, release and migration of a waste rock block through the ore in a cave mining operation and stability of rock mass blocks in open pit and underground mining was investigated.