Preparation of undisturbed soil hollow samples brings a series of difficult problems to the experimental researches on mechanical properties of soil. Due to the influences of coring operation disturbance, the reliability of experimental research on mechanical properties of undisturbed soft clay under complex stress path need to be further improved. A new device and method for preparing soft clay sample are designed based on the traditional mechanical method. It has a desktop water drill, a detachable drill bit, and a sample barrel. It is easy to operate, has good quality, and has less disturbance to soil samples. It can quickly prepare a large number of hollow cylindrical samples. An undrained shear test on the cylindrical specimen of undisturbed soil under the deflection path of the principal stress axis is carried out using the hollow torsional shear apparatus (HCA). The changing curve of pore pressure and cumulative strain through dynamic test can be plotted. The study shows that the mechanical properties of the soil samples produced under complex stress conditions are more reliable and meet the test requirements.