This study aimed to evaluate the pressure difference distribution across the escape stair in a 24-story stairwell. A large eddy simulation (LES) method was used to model the pressure in a stairwell model with a set of simulation parameters using FDS (Fire Dynamic Simulator) software. Two configurations of fans involved single injection, and multiple fan injection is observed. A Single-injection fan is located on the highest point of the stair. The double injection system consists of two fans and is separated at 45 m at each other. When the fire alarm is activated, the pressurization fan automatically runs and delivered outdoor air to the stairwell. It is commonly acknowledged that the pressure would start to built-up in the stairwell before the occupants entering the stair by open the door. Besides, when the pressure is significantly high, the door is unable to be open from outside by occupants as a consequence. In order to overcome this issue, a pressure relief damper was then installed on the top of the stair. The numerical study shows possible pressure difference in the stairwell is about 50 and 95 Pa. However, a multi injection system has the advantages of proper pressure distribution along the stairwell. Performance-based design by using numerical computation is a valuable tool to predict the engineering system and presents a better understanding of how the system would perform in design.