Abstract: To study the influencing factors of performances of undersea jet trencher, a physical model is designed and the appropriate sand is selected as the substrate in model tests. The topographic deformation due to the scouring and the sediment concentrations are investigated to study the effects of the flowrate and travelling velocity of trencher on trench. The diachronic change process and reason of trench from initial digging to a balance state is analyzed. Experimental results show that flowrate has a certain impact on the depth of trench, and the travelling velocity of trencher has bigger impact on the width than the depth; at the earlier diachronic change of trench section, the trench depth is shoaled with the increase of trench width, which is caused by collapse, landslide and sands deposit of trench; while at the latter diachronic change of trench section, trench depth is shoaled but the trench width is hardly growing, which is related to the compactness of sand.