Stability analysis of a longwall, East 1 tailgate (E1TG) of Tabas underground coal mine is presented. The mine extracts coal by both longwall and room and pillar methods. The mine is designed to produce 1.5 million tonnes of coal annually. The roadways have a rectangular profile of 4.5m width and 3.5m height. The field investigations and the geomechanical characteristics of rocks showed that the rock masses are weak, requiring a suitable support system. The roadway is intersected by a major fault zone. To investigate the effect of the fault zone on roadway stability, in particular during the face retreat, extensive numerical simulations were carried out. It was found that the stability of the tailgate was severely affected by major structures such as faults and crushed zones. In addition to this, it was revealed that the situation gets worse during the face retreat. An optimised support system was determined.