A micro-droplet generator, comprising a chamber, enclosed by a casing, a spraying plate, having a plurality of spraying holes, a piezoelectric plate, a signal connector, and a storage tank. The piezoelectric plate is mounted inside the chamber, having a fixed end fastened on the casing and a free end performing a bending movement. The input port issues signals that cause the bending movement of the piezoelectric plate. The chamber and the storage tank contain liquid, with a constant difference of liquid levels in the chamber and the storage tank being maintained, so that negative pressure in the chamber is automatically regulated.