Abstract: Diffraction imaging is a technique that leverages the characteristics of seismic diffracted waves to gain insights into subsurface structures. Unlike traditional imaging methods that primarily utilize reflection waves, diffraction imaging offers enhanced spatial resolution, enabling a more accurate depiction of the microstructure. This capability is particularly significant for oil and gas exploration in complex carbonate reservoirs. The distinctive feature of diffraction imaging lies in its ability to harness information from diffracted wavefields, thereby maximizing the utility of seismic data and improving the identification of geological features like karst reservoirs. Due to the intricate nature of the subsurface medium and the various propagation modes of seismic waves, the energies associated with diffracted waves often overlap with those of reflection waves, creating challenges in accurately identifying and separating them. A wave-equation based diffraction imaging algorithm is proposed with stratigraphic dip angle as constrains. The results demonstrate that diffraction imaging holds significant promise for applications in complex karst reservoirs in the Southwest China.