The seafloor's uneven terrain induces turbulence, significantly affecting the hydrodynamic performance and wake dynamics of horizontal-axis tidal turbines (HATTs). A numerical method (LBM-LES) was developed by coupling the lattice Boltzmann method (LBM) with large eddy simulation (LES) to analyze HATT hydrodynamics. The method's validity was verified by comparing numerical simulations with experimental data. A detailed analysis was then conducted on the flow field and hydrodynamic performance of HATTs installed on terrains of varying elevations. The results reveal that the power coefficient (Cp) and thrust coefficient (Ct) increase exponentially with linearly increasing terrain elevation, ranging from 10.2% to 58% and 6.2% to 35.3%, respectively. Moreover, larger terrain features lead to more uneven pressure distribution on the blade surface and greater fluctuations in power and load. Higher terrains also exert a more extensive and pronounced influence on the flow field, inducing shear flow upstream and forming a recirculation region downstream. The velocity in the upper flow field increases both upstream and downstream, whereas the lower region experiences a significant decrease. The wake flow's velocity recovery rate is faster in the presence of terrain. Additionally, terrain-induced turbulence increases vortex formation, alters the helical structure of tip vortices, and causes wake meandering, which intensifies with increasing terrain size.