The invention is a kind of supersonic wave tangent line saw for hard and crisp material, which comprises the bed, longitudinal working slide flat, transversal work slide flat, piece bracket, diamond line saw, supersonic wave vibrating device, saw reciprocating motion mechanism and electricity control device, the supersonic vibrating device is fixed on the upper arm of the C type work bracket through screw, the electrical signal is transformed into mechanical vibration, and enlarges the amplitude through a pole, the diamond saw vibrates as wave, it generates reciprocating motion through cranked rod, C type work bracket, slide flat seat. The saw is in linear high frequency vibration state and reciprocating motion; the invention is simple and has a high productivity.