OBN (Ocean Bottom Node) seismic exploration technology, as an important innovative method in the field of marine oil and gas exploration, boasts significant advantages over traditional towed-streamer seismic exploration: it not only effectively compensates for the exploration blind areas that are difficult to cover by traditional technologies, but also provides richer subsurface geological information for oil and gas resource detection under complex geological conditions through its multi-wave and multi-component acquisition capability, wide-azimuth observation characteristics, and flexible mode supporting fixed-point and repeated observations. However, OBN seismic acquisition technology still has prominent limitations in practical applications: constrained by the engineering difficulty and cost control of seabed node deployment, the distribution of receiving nodes is often relatively sparse, and direct reception of seabed reflection signals is not possible due to the influence of acquisition geometry. These two issues directly lead to poor imaging effects of the seabed interface and shallow geological bodies in OBN seismic data, characterized by insufficient resolution and poor event continuity, which severely restricts the promotion and application of OBN technology in scenarios such as shallow oil and gas reservoir exploration and seabed geological hazard assessment.To address this key technical bottleneck, this paper proposes a downward-wave migration method based on shot-domain Kirchhoff integral. The core innovation lies in fully exploring the application value of multiple reflections—As signals formed by multiple reflections of seismic waves at subsurface interfaces, multiple reflections not only carry abundant information about the lithology and structure of subsurface media but also have a wider subsurface coverage than primary waves, which can just make up for the coverage shortcomings of OBN primary wave acquisition. The method achieves imaging optimization through three core technical steps: Firstly, the complex wavelet domain dual-sensor (hydrophone and geophone) merging technology is adopted, leveraging the time-frequency localization advantage of complex wavelet transform to accurately separate the upgoing and downgoing wavefields in seismic data, providing high-purity wavefield data for subsequent migration processing. Secondly, aiming at the common non-coplanar distribution of shot points and receiver points in OBN exploration, a step-by-step calculation strategy is designed to separately solve the travel time from the shot end to the reflection interface and from the receiver end to the reflection interface, effectively adapting to the complex undulating seabed terrain and avoiding imaging deviations caused by terrain effects. Finally, an optimized approximate weighting coefficient is introduced to simplify the calculation process, ensure processing efficiency, and maximize the retention of seismic wave amplitude information, achieving amplitude-preserved imaging and providing a reliable basis for subsequent reservoir parameter inversion.To verify the effectiveness and practicality of the method, this paper conducts forward model data testing and actual OBN exploration data validation: the forward model is constructed based on a typical complex seabed geological model, simulating exploration scenarios containing shallow faults, seabed uplifts and other geological bodies; the actual data is derived from an OBN acquisition project in a deep-sea oil and gas exploration block. The test results show that compared with traditional effective wave imaging methods, the method proposed in this paper uses water-layer first-order multiple reflections for migrated imaging, which can significantly improve the clarity of the seabed interface and the imaging resolution of shallow geological bodies, effectively fill the shallow blind area of OBN primary wave imaging, and ultimately obtain seismic profile data with better quality and more complete information. This research achievement successfully solves the core problem of poor imaging effects of the seabed and shallow layers in OBN technology, provides reliable technical support for oil and gas resource exploration under complex seabed geological conditions, expands the application scenarios of multiple reflections in seismic imaging, and strongly promotes the large-scale application and development of OBN technology in the field of marine oil and gas field exploration.