<p>This paper investigates the coupling characteristics of variable mass tank sloshing and ship motion. A full nonlinear numerical model of variable mass tank sloshing-external wave-ship motion coupling is established. Firstly, the coupled motion characteristics of tank sloshing and simplified hull in beam sea are compared, the time history of dimensionless roll angle agrees well with experimental results, and the accuracy of the numerical model is verified. Secondly, the effects of wave excitation and ship speed on the coupled characteristics of Korea Research Institute of Ships and Ocean Engineering very large crude carrier (KVLCC) tank sloshing and ship motion are discussed, and the influence of liquid filling rate on ship heave motion and pitch motion is discussed emphatically. The results show that during the tank filling, the sloshing pressure in the tank increases steadily, and the growth rate is positively correlated with the filling rate. At the same time, the ship pitch motion is less affected by tank sloshing, while the ship heave motion is evidently affected by tank sloshing.</p>