Abstract: Liquid sloshing is a very complicated phenomenon, and the existence of free surface makes this phenomenon being of strong non-linearity and randomness. In the simulation of liquid sloshing in 2D rectangle flume by SPH, there are two different load methods of external force which include loading external force onto the brim of flume and loading relative acceleration onto water particles directly. The numerical results are obtained by using these two methods with different amplitudes, different periods of external forces and different depths of water. Based on the analysis of vibration curves of liquid surface and frequency charts, and according to the comparison between numerical results and theoretical results, the similarities and differences between these two methods are discussed. Analysis results show that, firstly, loading external force onto the brim of flume is better than loading relative acceleration onto water particles directly when only the amplitude of external force is changed; secondly, both methods can reach the same results if the period of external forces closes to theoretical period, and when the period of external forces away from theoretical period, the former is better; thirdly, according to the analysis of vibration curves of liquid surface and frequency charts, the numerical results obtained by both methods are comparatively identical if just water depth is changed.