The conventional zero-lag crosscorrealtion imaging condition of reverse-time migration is subject to strong migration artifacts. This paper studies wavefield decomposition method under relatively complex subsurface. Although the method greatly suppresses the internal reflection noise, it is subject to residual noise. To suppress the residual noise, we apply a fan filtering on each wave field snapshot in space domain. The filtered wavefields are further decomposed into downgoing and upgoing components and into leftgoing and rightgoing components. The decomposition is carried on F-K domain.