The experimental device and scheme are designed to demonstrate the positive and inverse piezoelectric effects, in which the coupling relationships between mechanical energy and electrical energy are studied. A drive signal is applied to an electromagnet to stimulate vibration of piezoelectric bimorph. Both drive signal and generated electric signal are measured by an oscilloscope. Electric signal frequency is consistent with drive signal frequency, while electric signal amplitude is positively correlated to drive signal amplitude. Electric signal amplitude first increases and then decreases with drive signal frequency. The piezoelectric bimorph is excited by DC voltage source to produce deformation, which is amplified by an optical lever. The displacement of the piezoelectric bimorph is linear with the excitation voltage. Compared with the existing demonstration experiments, the conversion relationship between mechanical energy and electrical energy are investigated in this new designed experiment, which is helpful to make participants understand deeply of the principle of piezoelectric effects.