Yongjiang railway extra long-span cable-stayed bridge uses the orthotropic deck of steel box girder, and it is the first time that box girder used in the railway cable-stayed bridge, so it is necessary to do a research on the mechanics behavior of this structure with fatigue model test. The accuracy of the fatigue model test data results in the rationality of the test scheme, and the research contents of the test scheme are as follows: the finite element model of steel box girder has been built to analysis the characteristics of the stress distribution, and the fatigue-sensitive regions have been determined; three model schemes have been designed and compared under the principles of stress equivalence and economical efficiency , and the third model has been used as the final fatigue test model . The research result can provide reference for the design of fatigue test model scheme of the same kind of bridge.