Rapid population growth and urban development require more attention be devoted to the development of underground structures. However, the tunneling role is very important and it is a response to modern human needs. Tehran metro line 7 is the longest and deepest line in Tehran metro network and will excavate with earth pressure balance method. Since excavation the ground and support the tunnel face are two important duties of EPB machine, safe and economic operations depend on correct design and proportional to site conditions. The main objective of this study are analyzing parameters affecting the motor system(thrust force torque) and stability of the tunnel face. Due to the benefits of discrete element method, PFC3D code is used. For this purpose micromechanical parameters calculated from back analysis of insitu shear test, model Torque??, trust, face pressure compared with real data. By using numerical methods, the effect of penetration rate, cutterhead rotational speed, torque and thrust has been studied. Furthermore, the required necessary pressure to support the ground has been investigated and effect of the presence or absence of face pressure on stress and porosity distribution around face is analyzed. Adaptation values ??of the model with the real data indicate discrete element method is compatible. Also the possibility of modeling linear and rotational speed and the high mobility of the particles are the unique characteristics of this method.