Abstract—This paper evaluates deflection of the steel high rise structure due to the P-Delta effect considering the global slenderness of the whole structure. For easy and quick design only Linear Static analysis is performed and secondary loading effect is neglected in several underdeveloped and developing countries of South Asia. Using STAADPro v8i, 40 different model is simulated to observe the severity of the P-Delta phenomenon against standard Linear Static method. 4 different storey were combined with 5 varying span in both direction for varying the slenderness of the structure. During analysis lateral load imposed with UBC94 to perform the seismic events in two directions in the seismic moderate risk zone of Bangladesh using Bangladesh National Building Code (BNBC) corresponding coefficients however wind load is omitted to observe the seismic event effect in Steel high-rise structure solely assuming outcome decision would be same if the simulation would done for wind load also. This analysis reveals how crucial side of the structure generates different deflections with changing slenderness. Test results were evaluated by storey deflection (in mm) and percentage of variation of deflection was performed by comparing P-Delta outputs with Linear Static Method outputs.