Abstract: Three-dimensional mechanical analysis of a simply supported and grounded functionally graded piezoelectric rectangular plate with arbitrary distributions of the material properties has been made using a simply and effective method based on Haar wavelet. Since the good features in treating local singularities, the present method based on Haar wavelet is of high precision and efficiency for arbitrary distribution style, especially for the case that the material properties change rapidly in some structural region. Then the influences of the ratio of material constants on the top and bottom surfaces, different material gradient distributions on the structural response of the plate to mechanical or electrical stimuli are studied through numerical examples.