Abstract: Experiments are conducted to determine soil-breaking performance of the subsea hydraulic jet trencher, especially the soil-breaking of high-pressure submergence jet stream. In these experiments, soils with different shear strengths are obtained through soil mixing and testing. Soil-breaking performances of high-pressure submergence jet stream are subject to soil shear strength, jetting pressure, nozzle configuration and jetting distance. Freshwater is used to compare jetting strengths of circular and fan-shaped nozzles. Eventually, circular nozzles are selected for soil-breaking tests. With consideration to different jetting pressures, jetting distances and shear strengths of soil, jetting soil-breaking performances are measured under various conditions. 3D scanning is made for surface of soil after jetting to generate 3D images of broken soil, so as to analyze depths and widths of traces on the soil. In this way, jetting operations for specific conditions are defined.