A model study to investigate the sediment transport and cross-shore sediment flux near the shoreline is conducted for marine sand mining operation in Kyunggi Bay, Korea. A modeling effort using a 3-dimensional model, a wave model and wave-current sediment flux model has been applied to the study area. The ROMS (Regional Ocean Modeling System), SWAN and the Harris and Wiberg (2001) model represent the basic modules of the 3-dimensional hydrodynamics, wave transformation in shallow water and sediment transport respectively. The goal of the current study is to estimate the cross-shore sediment flux to quantify the erosion vulnerability of the shoreline by imposing various dredging intensity as inreal situation. Being the wave and current interaction considered, the sediment transport model adopts the outputs of ROMS and SWAN for any designated time and space in the computation field. The realistic hydrodynamic conditions and wave field obtained from 20-year wave statistics enhance the prediction of erosion process according to the water depth, offshore distance from the shoreline and dredging intensity (volume and frequency etc).