Abstarct: Due to the importance of tunnels and underground space in Minnig and Civil engineering issues, it is necessary to do extensive studies on this issue and its characteristic. There are two general methods for tunneling: mechanized and traditional (Drilling and Blasting (D&B)). The method of D&B in hard rock is still the most practical method. One of the risks of this method is failure due to excavation surrounding the tunnel. Due to the undesirable effects of the blast, such as increased maintenance costs, low tunnel progress rates, unforeseen stability issues, water flow, and reduced tunnel life, excavation damage zone measurement methods are still used.The purpose of this thesis is to investigate the effect of parameters affecting the dynamic damage in the rock mass around the tunnel. First, the theories of explosion and the mechanisms of failure due to explosion are mentioned. In the following, different methods of predicting these fractures are explained. Then, by expressing the advantages, features and principles of numerical modeling method, this method is selected to predict the damage zone due to explosion and then different tunnel drilling modes are simulated by UDEC software. The extent of the damage zone has been validated by analytical methods. In the following, sensitivity analysis to various factors affecting the damage zone has been performed. Factors such as rock cohesion and blast pressure have been found to play the greatest role and the internal friction angle of the rock plays the least role in the damage zone. Finally, in order to further investigate and simulate the rock mass conditions, the effect of changes in the geological strength index (GSI) of the rock in the extent of the damage zone has been investigated