The disclosure provides an efficient Monte Carlo molecular simulation method for calculating the liquid phase interfacial tension between benzene and water by improving Ewald sum, including the following steps: Step A: Initialize the simulation: two simulation boxes were prepared, both with the size (30×30×45 Å)-(35×35×55 Å), and 1200-2000 water molecules and 230-380 benzene molecules were respectively put on the grid point of the two boxes; Step B: Select the force field used for simulation; Step C: Perform Monte Carlo simulations on the two boxes separately under the canonical ensemble; Step D: Join the water box and the benzene box along the z direction to form a large box of (30×30×90 Å)-(35×35×110 Å), and run 50000-80000 Monte Carlo cycles to make the system reach equilibrium; Step E: After the system reaches equilibrium, the data was collected during the production period.