Cherenkov radiation and SmithPurcell radiation refer to the phenomenon of uniformly moving charged particles radiating electromagnetic fields outward, which commonly used in the design and fabrication of efficient and controllable terahertz light sources．Due to the limitations of complex theoretical deduction and experimental exploration, students find it difficult to form clear physical images in classroom learning. This article uses COMSOL software to study the above two phenomena and quantitatively provides the influence of charged particle velocity on the power, direction, and frequency of the radiated electromagnetic field. The simulation results are consistent with theoretical expectations. In addition, this article also presents a simple method for continuously tuning the radiation power and frequency of SmithPurcell radiation in the power range of 060 W and the frequency range of 1.21.8 THz, and gives the explanation of its physical mechanism. This work will help students form physical images of electromagnetic radiation from charged particles, and can also serve as a supplement to quantitative experimental design in related physics teaching.