Abstract: Submarine landslides serve as one of the primary triggering mechanisms and important courses for gravity flow sediment transport along continental margins worldwide. This study employs high-resolution 3D seismic data and multi-beam bathymetric surveys to investigate the geomorphological characteristics and seismic response features of the Tuaheni South submarine landslide complex offshore eastern North Island, New Zealand. Our research focuses on characterizing the fluid flow system adjacent to the landslide body and elucidating the role of free gas migration and gas hydrate distribution in landslide dynamics. The study delineates the spatial distribution of both the landslide body and bottom-simulating reflector (BSR), revealing distinct types and characteristics of fluid migration pathways. Key findings show that: (1) within gas hydrate-bearing sediments, tectonic normal faults serve as primary conduits for vertical free-gas migration toward the basal shear surface; (2) in hydrate-free zones, gas chimney structures provide direct pathways for free-gas ascent to the landslide base. Accumulation of free gas at the basal shear surface may generate localized overpressure. We proposed that the sedimentary strata functioned as a valve-like system, cyclically regulating pore pressure accumulation and release during landslide movement and stabilization, which might promote the outbreak of the slow slip event in the Tuaheni South landslide complex.