Taken a membrane-type LNG bunker of a refrigerated container ship for example, and considered the coupling effect of ship motion and sloshing in LNG bunker, the LNG sloshing pressure in the bunker is calculated in the time domain based on the potential flow theory. The oscillating load acting on the bulkhead is decomposed into the impulse pressure and non-impulse pressure. The time-varying LNG pulse pressure is regarded as the virtual additional mass to couple the ship motion, and the sloshing pressure of LNG bunker is analyzed by the numerical simulation method. The results show that the sloshing pressure increases greatly when the bunker is farther from the midship with a higher center of gravity. The research can possess certain reference significance for the sloshing pressure calculation of other types of LNG bunkers.