A set experimental device,which can carry out laboratorial research about flow pattern and pressure drop law under suction is designed.Based on analysis and discussion about experimental phenomenon and experimental results,the following conclusions are drawn.There are three flow patterns to fluid under the action of suction in different conditions:water single-phase flow,air-water two-phase flow,air single-phase flow.The water level is ascending when water single-phase flow in store water bottle,and immobile when air single-phase flow,and descending when two-phase flow.Vacuum pressures are changed along flow direction,and ascending fluid's average pressure falls are unequal in different flow pattern.Fluid's flow pattern is air-water two-phase flow under the action of suction and groundwater descends that accord with project practice,and there isn't negative exceeding pore water pressure in vacuum preloading ground.Flow pattern and flow character are distinctly seen in pipeline,and experiment device is simple and redone easily.It can provide experimental condition to research flow rule of fluid in vacuum preloading ground.