The motion model of gas and liquid slug in pulsating heat pipe was suggested through forces analysis on it.The model was solved numerically.The performance of liquid slug pulsating motion with time was observed and some important factors influencing liquid slug moving were obtained.It is illustrated that liquid slug oscillates around a changing position.The pulsating motion was influenced greatly by initial pressure and tube diameter.The liquid slug oscillates randomly in the situation with lower initial pressure and small diameter

but the altitude of oscillating increases with initial pressure and diameter.