Abstract: An in-depth understanding of the spatial heterogeneity and driving mechanisms underlying Gross Primary Productivity (GPP) variations is of great scientific significance for vegetation restoration and near-natural carbon sequestration measures.Existing studies on the spatial patterns of watershed GPP have primarily been conducted at the grid scale,focusing mainly on qualitative descriptions and lacking intuitive representations of spatial relationships.This study innovatively integrates the Horton-Strahler (H-S) stream ordering method into the analytical framework of watershed-scale GPP spatial patterns.Taking the H-S stream order as the core linkage,we constructed a systematic analytical framework coupling H-S orders,GPP spatial characteristics,and driving factors,providing a new technical pathway for precise characterization of watershed GPP spatial patterns.Taking the Yangtze River Basin as the study area,we selected three GPP products to systematically analyze the spatial distribution characteristics and variations in river reaches of different H-S orders from 2001 to 2018.This study further explores the driving mechanisms of GPP variation relative to land cover types and hydrothermal conditions (precipitation and temperature) across different H-S orders.The results show that:(1)GPP variation characteristics of different H-S orders exhibit distinct spatial differentiation and a consistent response to H-S orders;(2)GPP variation characteristics show significant correlation and consistency with land cover types;(3)Climate attribution fractions of GPP exhibit distinct spatial patterns across H-S orders.Precipitation acts as the dominant driver of GPP spatial variation for H-S orders 7 and 9,whereas precipitation outperforms temperature in affecting GPP spatial variation for other H-S orders;(4)Hydrothermal constraints on GPP have their own optimal coupling intervals for precipitation and temperature across H-S orders.This study offers a novel analytical perspective for watershed-scale GPP spatial patterns research,and provides a scientific basis for regional carbon cycle regulation and ecological restoration.