Sediment incipient motion is the first stage of the whole process of local scour around a marine infrastructure. Most previous investigations ignored seepage flow on the mobility of bed particles except a recent study including the effects of vertical seepage flow in the prediction of sediment motion. In this paper, a new model further combing the vertical and horizontal seepage force is proposed. The modified Shields parameter by considering two-dimensional seepage is derived. Then, the effects of wave and soil parameters on sediment incipient motion are analyzed. It was found that lower water depth and saturation, higher wave height, shear modulus and permeability, will remarkably increase both modified Shields parameters and the gaps of the results considering vertical and two-dimensional seepage forces. Therefore, the horizontal seepage can not be ignored.