Mechanized longwall mining is considered as one of the best choices for excavating low dip coal seams. In this method, the position and movement of power supports play an important role in production, safety and performance. In this article we surveyed stress condition around the longwall face based on a numerical simulation using FLAC3D software. Then the effect of stress distribution and geomechanical condition of roof and floor strata in longwall face on power supports function has been studied too. As a case study we chose First panel of mechanized Tabas coal mine in Iran. The study result shows that instances like increasing of power support pressure on roof, irregular stress distribution pattern, situation of roof cavability and also geomechanical quality of floor are all effective on how the power support system functions. The approach that has been used in this paper could be considered as a new systematic observational method, especially for second panel of Tabas coal mine.