In order to avoid the problems of instability and fatigue failure which may occur in extreme cases due to ignoring the calculation of deck system in the checking calculation of steel bridge, firstly, the space design theory of steel bridge is introduced, and the point of view that the strength and fatigue checking calculation of deck system of steel bridge is proposed. Then, taking continuous steel box girder bridge as an example, the stiffness flexibility of stiffeners is judged, the shear lag reduction coefficient and instability reduction coefficient are calculated, and the superimposed stress of the first system and the second system is obtained, and the calculation is carried out according to the superimposed principle. Thirdly, the fatigue models Ⅰ and Ⅱ are established, and the anti-fatigue calculation of steel box girder bridge is completed. Finally, the web and support stiffeners are checked according to the specification. The results show that closed stiffeners should be used in the bridge panel of the box girder in the compression zone. The maximum compressive stress of the second system obtained from the analysis theory of steel bridge cannot be ignored. Attention should be paid to vehicle load limit in operation; The calculation and analysis process is instructive to the design of the same type steel box girder.