Abstract: Relativistic electron bunches can generate THz wakefields through dielectric lined waveguide (DLW), which can be applied to witness bunch acceleration and longitudinal phase space manipulation of the driving bunch itself. In recent years, DLW-based THz wakefield techniques have attracted considerable interest because they naturally match the sub-picosecond duration of relativistic electron bunches and are capable of providing gigavolt-per-meter accelerating gradients. Compared with conventional RF (radio frequency)-based accelerating structures, they offer the advantages of compact size, wide tunability, and the possibility of passive beam-driven operation. Based on the bunch parameters of the Wuhan Advanced Light Source (WALS) injector, two relevant aspects of study were carried out. First, utilizing the 50 pC bunch parameters originally designed for external injection into laser plasma acceleration, numerical simulations were performed to conduct parameter scans and comparative analyses of rectangular DLW and metallic corrugated structures. The simulations covered a broad range of structural parameters, and the wakefield potential, frequency spectrum, and beam-structure coupling efficiency were used as evaluation criteria. On this basis, a dielectric-metal hybrid structure was proposed, and the results show that its wakefield strength surpasses that of the conventional structures. In particular, the hybrid structure combined the high-gradient capability of dielectric materials with the robustness and versatility of metallic corrugated structures, leading to enhanced field amplitudes and improved bunch stability. Such a configuration is expected to be beneficial for both single-bunch acceleration and multi-bunch beam manipulation. This provides a new scheme for THz wakefield generation and longitudinal phase space manipulation. Furthermore, directly addressing the practical demands of the injector under high-charge (1 nC) operation at WALS, DLW was introduced as an energy dechirper following the bunch compressor. At an average bunch energy of 270 MeV, effective compensation of the longitudinal correlated energy spread has been achieved. The numerical results indicate that the dechirper can reduce the correlated energy chirp by more than 50%, significantly improving the longitudinal energy uniformity across the bunch. By mitigating this correlated energy spread with the DLW, subsequent accelerating sections after the bunch compressor can operate at peak gradient without sacrificing beam quality, thereby improving the overall accelerating efficiency of the LINAC injector. This work demonstrates not only a new wakefield structural design but also a systematic evaluation of the energy dechirp function under realistic LINAC injector conditions. The results confirm the application potential of DLW in the WALS and indicate that such structures could also be applied to other advanced light sources and free-electron laser facilities. In a broader context, the proposed approach provides theoretical support and practical guidelines for implementing advanced wakefield-based beam manipulation techniques, contributing to the ongoing development of high-brightness electron bunches and compact accelerator technologies.