A two-dimensional numerical simulation model between a rotating detonation combustor (RDC) and a turbine is constructed to study the flow field structure and coupling characteristics under different detonation wave propagation modes. Results show that the turbine’s feedback pressure will negatively impact the stability of the rotating detonation wave, and the adverse effect decreases with the increase of the number of detonation waves. In single-wave mode, compared with counterclockwise propagation, the pressure oscillation attenuation and total pressure loss increase when the detonation wave propagates clockwise through the turbine guide vane. However, with the increase of the number of detonation waves, performance differences caused by the opposite direction of detonation wave propagation gradually decrease. Although RDC increases the total gas pressure, it intensifies the flow field oscillation and significantly reduces turbine efficiency. When the RDC operates in two-wave mode and the detonation wave propagates counterclockwise, the overall performance of the engine is the best, the specific power gain is 27.9%, and the instability is 5.0%.