To provide reference for the development of new generation reusable launch vehicles， the detailed characteristics of SpaceX Starship are summarized. The typical volume of fraction （VOF） method is employed to perform a numerical simulation of 3-D unsteady flow in liquid oxygen tank during the Starship’s reentry stage. The liquid oxygen （LOx） sloshing characteristics under complex accelerations are analyzed. The simulation results show that a low-frequent （<0.6 Hz） and a high-amplitude （i.e. axial center of mass displacement up to 20%） sloshing occurs during the Starship’s landing stage. A large amount of air entrainment appears at the bottom of the propellant tank， which may bring disasters to the rocket engine.