The main objectives of this research are to study experimentally, analytically and numerically the effectiveness of the proposed external strengthening techniques to resist punching shear of reinforced concrete flat slabs. The finite element (FE) analysis software program (ANSYS V. 19) was used to create the models and investigate the effects of some parameters on punching shear of reinforced concrete flat slabs. Ten variable parameters are taken into consideration during study full scale flat slab models to account the influence of: (1) concrete compressive strength fcu; (2) reinforcing steel yield strength fy; (3) slab thickness (ts); (4) shear studs and stirrups diameter (Db); (5) shear studs (stirrups) spacing /ts ratio (Sb/ts); (6) shear studs stirrups spacing/ts ratio (D/ ts); (7) main steel ratio/ max (  / max); (8) top steel ratio/ max (` / max); (9) drop thickness/ts ratio (td/ ts) and (10) drop diameter/ts ratio (Dd/ ts).The numerical results were compared with the analytical results calculated from ECP 203-2017 [1] and ACI 318-19 [2]. The comparison showed a great match between the numerical results and the results of the two codes, especially ACI 318-19 [2].