The concept of effective stress and effective stress equation are fundamental for establishing the theory of soil mechanics and poromechanics. However, up till now, the physical meaning of effective stress has not been explained clearly, and the theoretical basis of effective stress equation has not been proposed. Researchers have not yet reached a common sense on the feasibility of the concept of effective stress and effective stress equation for unsaturated soils. Considering the effect of pore fluid pressure and the external forces excluding pore fluid pressure on the soil skeleton...