In this study, molecular dynamics simulations are performed to estimate the equilibrium pressure of liquid confined in nanopores. The simulations show that pressure is highly sensitive to the pore size and can significantly change from absolute positive to absolute negative values for a very small (0.1 nm) change in the pore size. The contribution from the solid–liquid interaction always dominates the pressure in the first liquid layer adjacent to the surface and the sensitiveness of pressure on the pore size is dependent on the atom distribution in the liquid layers. A surface influence number S is introduced to quantitatively characterize the degree of the confinement. At constant system temperature, the S number decreases with increasing pore size based on a power-law function. In nanopores with large S number, the pore liquid pressure is found to be independent of bulk liquid pressure, whereas in nanopores with small S number, the pore pressure is dependent and increases with bulk pressure.