乾隆于1749-1751年间在北京西郊进行西郊泉山导引和昆明湖库域建设，旨在为京郊营田、京师漕运提供水利支持。本文考察乾隆时期北京西郊水源整理的源起、过程与困境，在自然环境与政治语境中解析权力、技术与自然的互动逻辑。第一部分依循元明清时期畿辅水学与水政的宏观脉络，探讨乾隆西郊水源整理的生态背景、政治意图与思想渊源。第二部分聚焦于水源整理的实践过程，反思这一水利工程所面临的生态与道德困境。乾隆年间的京畿水利建设未能突破水源限制，平衡农田、园林、漕运的用水需求；惠农利漕的治水初衷因园林建设之重费而陷入质疑。“治水”并非权力与技术对自然的完全控制，而是在生态与道德的边界之中，寻求自然与政治间的平衡。This thesis examines the cause, process and dilemma of the water conservancy project in the western suburb of Beijing launched by Emperor Qianlong. Chapter one discusses the ecological, political and intellectual background of Qianlong’s water control in the context of hydraulic practice in Jifu area. Chapter two evaluates the effects of Qianlong’s water conservancy program within the micro environment around the Kunming Lake. It argues that imperial hydraulic enterprise, as the interaction between power, technology and nature, was rather striking a balance between politics and nature than acquiring the total control of water without any ecological and moral limitations.