Collaborative legislation for watershed governance constitutes an important rule-of-law approach to addressing the challenges of transboundary watershed governance, and the legislative practice in the Chishui River Basin provides a typical case. At present, the environmental management model organized around administrative divisions runs counter to the natural geographical attributes of river basins. The spatial effectiveness of local legislation cannot cover the entire basin, and the overall interests of the basin are difficult to be effectively safeguarded, which highlights the necessity of collaborative legislation for watershed governance. To achieve the goal of collaborative governance, collaborative legislation for watershed governance should focus on three core elements: collaborative mechanisms, collaborative matters, and the internal heterogeneity of the basin. However, a review of the collaborative legislation for watershed governance of the Chishui River Basin reveals several problems, including imperfect institutional design of collaborative legislation, a lack of unity and systematic arrangement of collaborative matters, and insufficient consideration of internal differences within the basin. Therefore, it is necessary to improve the ecological compensation mechanism and establish a collaborative assessment mechanism; strengthen the unified and systematic design of collaborative matters; and clarify different legislative priorities according to the internal heterogeneity of the basin. These measures aim to ensure incentive compatibility among collaborative actors, shared responsibilities, and benefit-sharing, thereby enhancing the effectiveness and stability of collaborative watershed governance.