Abstract: To simulate the unloading sampling process of marine soil, laboratory triaxial tests are carried out with the marine soil from the seabed, and the advanced GDS triaxial test instrument is employed to remold the marine soil sample under the same initial pressure conditions as those of the field soil, thus the properties of marine soil, e.g., cell pressure vs soil volume change, are investigated. In general, the saturated soil sample volume change is approximately measured by the volume change of the back pressure controller; the correction of volume change due to compressibility of high-pressed water is also taken into consideration in this study. The test results with different test conditions, such as different loading and unloading cycles, as well as different unloading times, show that the high-pressure test results are not sensitive to these conditions. The unloading tests on different initial confining and pore pressures show that soil volume change increases with the initial pore pressures, etc. The general test features of the unloading sampling process are concluded in this study. The high-pressed soil sample swells slowly in the early unloading process, and then becomes steadily quicker, and the quickest in the end. The results of all the test conditions only differ from each other in the middle stage of the unloading process, not at the beginning or at the end stages, which is somewhat different from that of low-pressed soils.