To analyze the effect of fire temperature gradient on shear lag effect of the corrugated steel web composite box girder, based on the energy variational method and combined with the temperature stress theory of steel-concrete composite beams, this paper deduces the theoretical analysis formula of shear hysteresis-effect of composite box beams with corrugated steel webs under fire temperature gradient, and establishes the thermal coupling numerical analysis model of composite box beams with ANSYS finite element software to verify the applicability of the theoretical formula. The variation of shear lag effect of composite box girder with corrugated steel web under different fire time and load ratio is further analyzed. The error of the analytical solution, finite element numerical solution and measured values of the shear lag effect of the composite box girder with corrugated steel webs derived in this paper is less than 7%, which indicates the good applicability. Under fire, the shear lag effect of composite box girders is significant, and it becomes more pronounced as the temperature increases. The maximum shear lag coefficient λ_max of the composite box girder increases first and then decreases with the increase in fire time. The shear lag effect of the composite beam decreases with the increase of load ratio. λ_max is greater than that under normal temperature when the load ratio is 0.2 and 0.3, and less than normal temperature when the load ratio is 0.4. The research results can provide a reference for the analysis and calculation of the shear lag effect of corrugated steel web box girder under fire temperature gradient.