Abstract: The conclusion is given that the modal control forces produced by point piezoelectric actuators on flexible beam and frame are direct proportion to the modal strains at the places pasted piezoelectric flakes,based on modal control theory and Euler Bernoulli point force model of point piezoelectric actuator.According to the conclusion,the maximal modal force rule of point piezoelectric actuator place optimization has been put out that point piezoelectric actuator should be placed at the position where each order modal strain is maximal.The computer emulating results of intelligent flexible beam and frame show that the rule is correct and effective.