Under global warming and climate change, coastal regions, including China, are increasingly vulnerable to typhoon damages. With typhoon gales, heavy rainfall, and storm surge, typhoons cause great economic losses and casualties to the coastal communities of China every year. Therefore, it is of great academic and social values to study the generation mechanism and movement mode of typhoons. However, accurately predicting the potential storm surge that a typhoon in growing can cause is a very challenging task. During the evolution of typhoons, the ocean-atmosphere (sea-air) interface has strong exchange of mass and energy. At the same time, various physical fields, such as wind, pressure, flow and wave fields interact strongly with each other. To accurately simulate the typhoons and the corresponding storm surge, the air-sea interaction is not to be neglected. Hence, it is very important to establish a reliable prediction model of sea-air coupling. In this paper, we established a fully two-way coupled sea-air model for South China Sea (SCS) by applying the mesoscale atmospheric model named WRF, the regional ocean model named ROMS, and the model coupling toolkit (MCT). In this complicated coupled sea-air model, WRF transfers the sea surface stress, net heat flux, sensible heat flux, latent heat flux, shortwave radiation flux, and longwave radiation flux to ROMS through MCT coupler. In turn, ROMS transfers sea surface temperature (SST) to WRF. By applying the fully coupled WRF-ROMS model, the storm surge induced by Typhoon Kai-tak, 2012 in the SCS is simulated and analyzed in detail. The computational capability and reliability of the coupled WRF-ROMS model are well verified by comparing the simulated typhoon track, and corresponding intensity and strength with the observed values in the field. The verification data show that the two-way coupled model has better accuracy and advantage in simulating typhoon dynamics than the one-way coupled model. Subsequently, the validated two-way coupled model is used to systematically study the atmospheric dynamics and the storm surge induced by typhoons in SCS. By analyzing the numerical simulation results, the wind and pressure field, as well as the spatial and temporal distribution characteristics of storm surge and wind-induced current, are obtained. We found that the spatial distribution of the wind, storm surge and flow fields caused by Typhoon Kai-tak is asymmetrical. The intensity of the typhoon on the right side of track is stronger than that on the left. Moreover, compared with the temporal evolution of typhoon, there is some delay in the evolution of the storm surge and the wind-induced current in the near shore.