Superradiant free-electron lasers (FELs) can significantly reduce the saturation length and produce high peak-power radiation pulses. However, this mechanism places stringent demands on the precise longitudinal micro-bunching of the electron beam. In this paper, we propose a compact, high-power terahertz (THz) superradiant scheme based on electron bunch trains induced by dielectric wakefield modulation. The electron beam acquires a THz-frequency periodic energy modulation in a dielectric-lined waveguide (DLW), which is converted into density modulation by the linac and chicane. In the non-ultrarelativistic regime, longitudinal space-charge oscillations (LSCO) introduce coupling between the longitudinal and transverse beam dynamics, increasing the complexity of beamline optimization. Therefore, a multi-objective optimization approach based on NSGA-II is used to determine the beamline configuration. Numerical simulations demonstrate that the proposed scheme generates bunch trains with tunable spacings ranging from 1 ps to 2 ps, with a maximum bunching factor of 0.4 at the fundamental frequency. Further analysis indicates that, after microbunch formation, LSCO contribute to a reduction in energy spread, improving beam quality. In addition, a one-dimensional FEL code is developed to investigate the radiation performance of the pre-bunched electron beam within the undulator. Simulation results show that the radiation frequency is tunable over the range of 0.5–2 THz, with a maximum radiation energy of 47.7 µJ for an electron beam with an energy of 10 MeV and a charge of 150 pC.