Based on an orthotropic steel deck of a long-span suspension bridge in Three Gorges reservoir area, a 1∶2 scaled-down fatigue experiment in design life span and limit life span was carried out to explore the fatigue behavior of critical details in the steel orthotropic decks of steel box girder suspension bridge, which is sensitive to fatigue crack under repeated loads. The fatigue experiment results show that the stress fluctuation ranges of critical details of the fatigue model are very small after 2 million times of cyclic loading in design life span, displacements of measure points of the fatigue model have good symmetry and recoverability in the static loading and unloading process, and there are no local fatigue cracks and damage during the experimental process of the design life span. It is considered that the orthotropic steel deck of this experiment in good welding and normal maintenance will not appear cracking in the design life, and fatigue performance of the orthotropic steel deck meets the design requirements and has some safety reserve.