Abstract: Aiming at the problem that the rotational response is difficult to measure in structural identification, an approximate algorithm based on Neumann expansion theory is developed for rotational response identification. The rotational response cannot be calculated according to structural displacement response based on the static condensation algorithm in FEM analysis since the stiffness parameters are unknown in structural identification. When the difference among structural parameters are not big, the inverse matrix is available by introducing Neumann expansion to get the information on rotational response. Theoretic analysis and numerical examples are given to illustrate that the approximate algorithm based Neumann expansion is applicable when structural parameters differ not widely from each other, and an accurate solution can be obtained if the structural parameters are all the same. The norm errors of the approximate algorithm is generally small, while the smaller the absolute value is, the greater the component errors will be.