The stiffness of microstructure is an important parameter of the microsensor. It is usually obtained by FEM approach, which is difficult to give an analytical expression. This paper reports on a biaxial microaccelerometer with the crab-leg flexural suspension. Its stiffness is carried out by using force method and Castigliano’s theorem. During the deduction, we neither introduce the other assumptions nor design the special dimension. So this methodology is strict in theory, and can be extended to analysis for the displacement and stiffness of the symmetric and statically indeterminate microstructure.