With the rapid development of terahertz technology, people are increasingly interested in its various applications in communications, spectroscopy, and sensing. The basis for the development and application of terahertz technology is high-performance terahertz sources. Traditional terahertz sources are large in size and require high-power power supply to drive and are difficult to adapt to the development of integrated terahertz technology. Therefore, there is an urgent need to develop micro-terahertz sources with new mechanisms. This paper studies a new type of miniaturized free electron terahertz radiator, which realizes the excitation of terahertz waves based on the interaction of free electrons and the terahertz waves excited in the grating dielectric waveguide structure. This research provides new options for developing efficient on-chip terahertz radiation sources and expanding advanced terahertz applications.