The reaction process of copper-aluminum displacement in agar gel was observed at the microscopic level with a stereomicroscope; pine-like branches of copper crystals growing from aluminum surface into gel at a constant rate were observed. Students were asked to make hypotheses on the pattern formation and design new research approaches to prove their hypotheses. Results of the experiments designed by students well proved the existence of microcells in reaction system, which caused continuous growth of copper branches. The whole experimental teaching process motivated students by stimulating their interest and enthusiasm.