Abstract: The Kuroshio Extension in the Northwest Pacific Ocean is a unique region where the Kuroshio and Oyashio currents converge, creating a dynamic environment with diverse water masses and complex hydrodynamic processes. This region plays a critical role as a global carbon sink and a habitat for economically significant marine species. Despite its importance, the spatial distribution of nutrients and the mechanisms regulating them remain poorly understood. Based on in situ observations of the entire water column conducted in May and June 2021, this study provides a systematic analysis of nutrient distribution patterns and their influencing factors in the Kuroshio Extension region. Results indicate a south-to-north increase in nutrient concentrations in the upper ocean (＜1000 m). In the subtropical and Kuroshio Extension Subtropical (KES) zones, surface waters, influenced by North Pacific Tropical Water, show nutrient depletion, while subsurface waters within the Subtropical Mode Water exhibit lower concentrations and weaker vertical gradients. In contrast, the surface waters of the Kuroshio Extension Northern (KEN) zone, impacted by Pacific Subarctic Upper Water, display higher nutrient levels. Subsurface waters, dominated by North Pacific Intermediate Water, also have high nutrient concentrations and pronounced vertical gradients. The vertical turbulent diffusive nutrient flux is notably weaker south of the main axis than the north, limiting the upward transport of nutrients from deep, nutrient-rich waters. These findings highlight the role of water mass properties in shaping nutrient distribution, offering valuable insights into the biogeochemical dynamics of the Kuroshio Extension region.