The structural design of a mechanical temperature-driven shut-off valve used in the water and steam sampling device of a power plant is designed using a Iventor drawing software. A NiTi shape memory alloy with high temperature-sensitivity is used as the driven spring to control the opening and closing of the valve. In addition to the design of the structures and common parts of the shut-off valve, the mechanical calculation and parameter-design of the driven spring are also carried out. The valve is unimpeded and can take water-steam samples under the normal state. When the temperature exceeds a 49 oC, the valve will be shut off due to the driven spring extends and the water intake will stop. When it is necessary to take water-steam samples again, it can be reset manually.