Some retrofitted methods are introduced, and in these retrofitted methods, a strengthening case of using the sandwich plate system (SPS) to strengthen the orthotropic steel bridge deck of a suspend bridge was studied. A local finite element model is established by ANSYS based on an orthotropic steel bridge deck sample, stress distribution of deck due to the wheel load of the vehicle defined in China current code were analyzed under different loading conditions, and the strengthening effect with SPS was evaluated. The influence of the thickness and elastic modulus of elastic sandwich on the transverse stress of deck was analyzed. The results show that, compared with the orthotropic steel bridge deck before strengthened, the stress peak is decreased obviously without new welding residual stress be generated, and the fatigue resistant of bridge deck is increased apparently after the deck strengthened by SPS. The variation of the thickness and elastic modulus of the elastic sandwich have little influence on the stress behaviours of the orthotropic steel bridge deck.