This　paper　proposes　a　novel　method　for　increasing　the　distortional　frame　rigidity　of　off-rail　box　girder　bridges　for　cranes　by　reinforcing　the　diaphragm　with　staggered　truss.　The　study　starts　by　using　the　Matrix　Displacement　Method　to　determine　the　shear　angle　of　the　staggered　truss　diaphragm　under　two　assumptions:　hinge　joint　and　rigid　joint.　To　obtain　closed　-form　solutions　for　the　transversal　and　longitudinal　deformations　and　warping　stress　of　the　crane　girder,　the　study　employs　the　Initial　Parameter　Method　and　considers　the　compatibility　of　shear　deformation　at　joints　between　the　diaphragms　and　the　girder.　The　theoretical　solutions　are　validated　through　finite　element　analysis,　which　also　confirms　that　the　hinge-joint　assumption　accurately　represents　the　shear　angle　of　the　staggered　truss　diaphragm　in　girder　distortion.　Additionally,　the　study　conducts　extensive　parameter　analyses　to　examine　the　impact　of　staggered　truss　dimensions　on　distortional　stress　and　deformation.　Furthermore,　the　study　compares　the　distortional　warping　stresses　of　crane　girders　reinforced　with　staggered　truss　diaphragms　and　those　reinforced　with　perforated　ones,　emphasizing　the　importance　of　incorporating　stagger　truss　in　diaphragms.　Overall,　this　paper　provides　a　thorough　evaluation　of　the　proposed　approach＇s　effectiveness　in　enhancing　the　distortional　frame　rigidity　of　off-rail　box　girder　bridges　for　cranes.　The　findings　offer　valuable　insights　into　the　design　and　reinforcement　of　diaphragms　using　staggered　truss　to　enhance　the　structural　performance　of　crane　girders.