Abstract: Water systems are one of the core elements in cartography. However, river and lake network data often lack precise topological structures, while contains complex skeletons and unclear hierarchical classifications. These issues complicate the grading and width transition of water system data, making it challenging to meet the timeliness requirements for data processing and visualization in scenarios like emergency mapping. To address these challenges, we first introduce an automated method for constructing and grading water system structures, based on water system topology and the upstream tracing length of river segments, specifically designed for complex water systems. Secondly, a method for calculating and visualizing gradual width changes in water systems using the convex angle arc approach is presented, which is built upon the graded water system data. Finally, using Wuhan City and Jiangxi Province as study areas and referencing relevant map data, we evaluated the proposed methods′ effectiveness in water system grading and gradient representation. Experimental results demonstrate that the proposed approach can accurately identify the main and tributary structures of water systems, achieving a gradient rendering effect that supports automated cartography needs. This method effectively addresses numerous challenges in traditional cartography related to water system grading and gradient rendering, significantly enhancing the efficiency and accuracy of water system data representation. It provides valuable technical and methodological support for intelligent and rapid map creation.