Abstract: The orthotropic steel bridge decks are easy to suffer from fatigue cracking under the traffic load. In this paper, a new-type composite bridge deck system, which is composed of an orthotropic steel deck and thin RPC (Reactive-Powder- Concrete) ultra-high-performance concrete layer, is proposed to solve this problem. With the adoption of the composite bridge deck system, the rigidity of orthotropic deck is enhanced, while the main structural mechanic performance is improved without increasing the dead load weight of the bridge deck. Analyses of a certain bridge with such composite bridge deck show that the stresses in steel bridge deck deduce greatly under the traffic load. Tensile stresses at the fatigue sensitive points of the steel bridge deck are decreased by 71.32% to 72.39%, leading to an elongated bridge’s fatigue life. Due to its high strength and high toughness, the thin RPC layer can completely satisfy the limited requirement of tensile stress of 10.08 MPa. The thin RPC layer can be used as a permanent structural overlay in steel bridge deck, and the risk of causing fatigue cracks of the steel bridge deck can be greatly reduced.