Abstract: The paper builds the model of piezoelectric flexible structures and calculates the mode frequencies using ANSYS software, and then, extracts the required modes by the method of model reduction based on the spatial H2 norms of modes. The optimal location of the piezoelectric patch is determined by applying the D-optimal design principle, which avoids the location’s randomicity as well as reduces the number of sensors/actuators needed to keep the controlling effect. Finally, the paper takes a piezoelectric cantilever beam as an example and calculates the step response curve of the system. The results show that this method generates better predictions than the ordinary modes truncation.