In order to further clarify the changing law of the sailing resistance of a ship in a navigable tunnel，this paper proposes a sailing resistance estimation formula for large ships and builds a physical model to carry out ship model tests to verify and analyze the formula.The results show that the measured resistance value and the formula have a high degree of fitting，and the verification effect is great.The change of the cross-sectional area of the tunnel water area has a greater disturbance to the sailing resistance，and the sensitivity of the sailing resistance to the cross-sectional area of the tunnel water area is higher than that to the ship speed.The sailing resistance is proportional to the square of the ship speed and decreases with the increase in the navigable section coefficient.