Robot-assisted therapy can provide effective rehabilitation training for stroke patients. The interfacial stress between the manipulator and the grasped patient's body is very important for a rehabilitation therapy robot. This paper presents a measurement method, which is able to decouple the measurement of the three-dimensional (3-D) interfacial stress components. To implement the method, interfacial stress sensors were fabricated based on plate capacitance and a superelastic material, while a high-resolution microcapacitance measurement circuit was developed based on a minimal system microprocessor and a programmable controller, and experiments are carried out by using a 3-D stress simulation equipment. The results show that the measurement circuit is capable of measuring a range of 1 fF–30 pF capacitance with a resolution better than 1 fF, and the sensor is capable of measuring Z-direction normal compressive stress at a range of ${\text{0-3.0}} \text{kgf}/\text{cm}^2$ with a sensitivity of ${\text{101}} \text{fF}/\text{kgf}/\text{cm}^2$ and X - and Y-direction shear stress at a range of $0-1.0 \text{kgf}/\text{cm}^2$ with a sensitivity of ${\text{118}} \text{fF}/\text{kgf}/\text{cm}^2$. This method can be applied to rehabilitation therapy robots to decouple the measurement of the 3-D interfacial stress components.