Abstract: To systematically analyze evolutionary characteristics and structural features of ecological and environmental protection policies in the Chishui River Basin, so as to reveal the policy logic and optimization directions for cross-provincial basin collaborative governance, by collecting policy texts related to the Chishui River Basin over the years and adopting quantitative analysis methods, we conduct an in-depth analysis from dimensions of policy intensity, institutions, types, themes, and instruments. The findings indicate that: ① Policy formulation has undergone three stages, exploration, incremental promotion and comprehensive advancement, with continuous growth in quantity and intensity, demonstrating a process in which Guizhou Province took the lead in pilot efforts, the central government provided emphasis and impetus, and Sichuan and Yunnan Province followed with responsive measures. ② The issuing authorities form a collaborative multi-authority network involving legislative, judicial and administrative bodies, with legislative and judicial institutions dominating horizontal issuance and governmental authorities dominating vertical issuance, and mutual complementarity is found in the vertical hierarchy. ③ Policies are categorized by effectiveness into three types, high-effectiveness documents (including regulations, decisions, approvals, etc.), medium-effectiveness documents (mainly various plans and measures), and low-effectiveness documents, which account for a relatively small proportion. ④ The goals and themes of policies are divided into four categories, manifesting diversified and systematic characteristics. At the central and provincial levels, the aim is to achieve cross-regional and cross-departmental coordination, while at the municipal and county levels, the focus is on expanding local interests. ⑤ Policy instruments are diverse but administrative mandate-based instruments are absolutely dominant, with pre-event guidance instruments being the primary means. Economic incentive instruments and multi-stakeholder collaboration instruments are relatively underutilized. The application of policy instruments becomes broader at lower administrative levels. Based on the above conclusions, it is suggested that we further strengthen inter-regional and inter-departmental coordination and cooperation, and gradually improve the policy network that integrates ecological and environmental protection with industrial and social development, design more innovative incentive-based policy instruments from the bottom up, enhance policy implementation safeguards, and ultimately achieve ecological prioritization and green development in the basin.