The present invention relates to a terahertz wave generator and a method of generating high-power terahertz waves using the terahertz wave generator. The terahertz wave generator includes a hollow spherical body, and a focusing lens installed in a cutout portion of the spherical body or an opening formed in the cutout portion, wherein an inner surface of the spherical body is coated with metal. In the method, frequencies having different levels are incident through the focusing lens or the opening to generate a plurality of air plasmas, and the air plasmas cause continuous focusing the metal-coated inner surface and hollow space of the spherical body, thus generating high-power terahertz waves. According to the present invention, a plurality of air plasmas is continuously generated, thus solving the problem in which the light intensity of terahertz waves generated using one air plasma is low.