By the solution-dropping method imitating the growth of stalagmite in nature, piezoelectric KNbO3 crystal was prepared onto a substrate by dropping metastable K2NbO3F aqueous solution. The transformation from K2NbO3F to KNbO3 was accelerated by separately dropping H2O2 solution at the same time. Under the conditions of K2NbO3F concentration of 4.2×10-2 mol/l, H2O2 concentration of 9mol/l, dropping rate of 1.7ml/min, dropping time of 2 h, and substrate temperature of 20°C, KNbO3 crystals of 2 to 5μm and polycrystalline film composed of KNbO3 crystals of < 1μm were grown at aqueous temperatures of 20°C and 60°C, respectively.