Abstract: A terahertz radiator is based on coherent Smith-Purcell radiation amplified by stimulation. The terahertz radiator includes an electron emission source configured to emit electron beams and a pumping source configured to emit pumping signals. The pumping signal interacts with a primary grating structure to obtain preliminarily bunched electrons. The preliminarily bunched electrons interact with the primary grating structure to generate coherent Smith-Purcell radiation. The coherent Smith-Purcell radiation and the pumping signals vertically resonate in a primary resonant cavity structure, so that the electron bunching density is increased, and in turn, the coherent Smith-Purcell radiation is enhanced. A positive feedback process is formed by free electrons and the coherent Smith-Purcell radiation, and the coherent Smith-Purcell radiation amplified by stimulation and periodic bunched electron bunches are obtained.