For lack of calculating formulas to design folded serpentine micro-cantilevers, this paper deduces calculating formulas to compute the deflection of a folded serpentine micro-cantilever and its spring constants in x, y and z directions combining the Hooke's law and the energy method. In deduction, it is found that the bending moment at the out corner will effect on the final results of the complex micro-cantilever seriously, so it can not be ignore in calculation. The spring constant of the folded serpentine micro-cantilever is calculated by finite element analysis using ANSYS software to validate the theoretic calculation. Compared with the finite element simulation, the relative errors of the folded serpentine micro-cantilever is 0.67%, 1.09% and 2.95% in the x, y and z directions respectively, and the values are all less than 3%. An image measurement system is established to measure the distortion of the cantilever. Experimental results indicate that the theoretic calculation values coincide with the measured values well. The formulas deduced for the folded serpentine micro-cantilever are logical, and the formula deduction can offer the gists for the computation and design of the folded serpentine micro-cantilevers.