Abstract: To build a stiffness filter function, the homogenization method is adopted to compute the cellular e-quivalent stiffness for square hole of various size. According to the discrete values obtained, the normalized least square method is applied to fitting the equivalent stiffness coefficients. With these coefficients, the least square method is used once again to fit the power exponent of the filter function for the ICM (independent, continuous, mapping) method. The obtained filter function reflects correctly how the equivalent stiffness varies with the size of square hole. Moreover, the obtained power exponent agrees with the published empirical value.