This paper aims to study numerically and analytically the effect of steel fibers on the behavior of reinforced lightweight concrete (RLWC) deep beams using strut and tie model (STM) and ANSYS program. The effect of nine parameters on the behavior: (1) effect of concrete compressive strength fcu; (2) effect of steel strength fy; (3) effect of beam depth; (4) effect of beam width; (5) effect of ratio (a/d); (6) effect of main steel ratio; (7) effect of web reinforcement; (8) effect of fiber content and (9) effect of fiber aspect ratio are studied. The numerical results obtained using STM and ANSYS V.15 computer program are verified by comparison with experimental results carried out previously published research and [1]. The performance of RLWC deep beams was investigated in terms of: (1) cracking load; (2) cracking pattern; (3) ultimate load; (4) failure mode; (5) displacement ductility and (6) toughness. It is concluded that both the Egyptian code ECP-2017[2] and ACI code 318-18 [3] are conservative in calculating the ultimate shear for RLWC deep beams.