High-precision micro/nano probe plays an increasingly important role in manufacturing and measurement. The multi-arm elastic mechanism that can produce deformation under the contact force is widely used in the design of probe. The striking feature of this mechanism is that multiple variables are coupled to each other and are not easily separated. However, the transfer matrix of probe, rather than a multivariable decoupling model, is widely used as a measurement model in traditional research. Transfer matrix appears as a “black box” and does not reveal working principles of probe. Our previous research proposed a 3D decoupling model. The 3D model presents the coupling relationship between input and output variables, and also finishes a theoretical explanation of complex features of 3D probe. Recent studies have found that this decoupling model has practical value in parameter and shape optimization of probe. As the optimized purpose, two indicators — sensitivity and compliance (reciprocal of stiffness) are proposed from the model. The increased sensitivity means the probe has a lower resolution requirement for the capacitive sensor used. High compliance of probe means small contact force between the stylus ball and workpiece. Excessive stiffness can cause excessive contact forces that damages surface of workpiece. Combined with theoretical model and finite element analysis (FEA), the key parameters affecting sensitivity and compliance of probe are extracted, and a new optimized elastic mechanism based on an original Hexflex mechanism. The new optimized probe has better performance with sensitivity, input compliance, output compliance increased by 78.6%, 48.4%, 157.7%, respectively.