Abstarct: The amount of coal production is an important parameter for industrial raising of each country. One of the newest and efficient methods for coal excavation is long wall mining. Although long wall mining was a method with high production and less proportional cost, but it had great connection to continuously production and non-stop process of excavation. Instability of face was the main reason for cease the coal production. The instability of face appear as spalling as the result of shear stress that applied on the face. Tabas coal mine use the long wall mining method for coal excavation. In this case study, excavations panels was in the 400-600 m level from surface that was so deep and strength of circuital rocks were in low classification, therefore in some points of panel, induced stress was greater than coal strength and after that spalling was happened. In this condition it’s necessary to specify the instable areas on face before excavation and prevention of spalling. In this study representing stability analysis on face using 3D numerical modelling program FLAC on E3 panel of Tabas coal mine. The quantity of mean shear strain on face that interpreted from numerical model was compared with critical shear strain that was obtained from Sakurai equation. The result shown the spalling occur on 6-10 m advance from first face right on primary roof caving and 18-22 m advance from first face for failure on tip-to-face span roof.