李長庚是乾隆末期至嘉慶年間極為活躍的水師將領，他官至浙江提督，並曾總統閩浙水師，長期承擔追剿海盜的任務，是嘉慶年間實際掌握大清絕大多數水師戰力的海防指揮官。他奔襲於浙江、福建沿海，穿梭於臺灣海峽兩岸，甚至追剿海盜到廣東，最後出師未捷，喪命於海盜狙擊手，其個人生涯可謂嘉慶朝抗擊海盜水師將領的代表。然而，關於他的早年活動和官場上的挫折，在各種傳記資料中多有過於簡略和為尊者諱的情形。此外，他出任浙江提督之後的史料雖然眾多，但在晚近的海洋史研究當中，海盜研究反而成為主體，對於抗擊海盜的水師將領，則較少受到關注。本文擬利用國立故宮博物院所藏宮中檔、軍機處奏摺錄副、上諭檔，中央研究院歷史語言研究所藏《明清內閣大庫檔》等官方檔案史料，以及私家著述：阮亨《瀛舟筆談》，焦循〈神風蕩寇記〉、〈神風蕩寇後記〉，和阮元《揅經室集》，及新近出版之《李忠毅公遺詩》等史料，探究李長庚生平及其海上生涯，並解析其君臣關係和官場際遇，盼能對嘉慶時期的海防問題稍做補白。

LI Chang-geng was a Chinese naval officer at the turn of the 19th century who has seen many battles in his life. He was the Military Commander of Zhejiang Province at the time of his death. He once commanded Zhejiang and Fujian's fleets and has been in charge of hunting down the pirates for a long time. During the Jiaqing Reign, he was the Qing Navy's most powerful commander taken charge of coastal defense. He battled in the coastal waters of Zhejiang and Fujian Provinces. His fleets were seen across the Taiwan Strait. He chased down pirates to as far as Guangdong province. Finally, in a lost sea battle, he was shot and killed by a pirate shooter. We may see him as the man behind Jiaqing Reign's war against pirates. However, his earlier life and his eventful career as an officer were often neglected or abbreviated by authors of his biography due to some kind of respect. Even though the historical records regarding his post-Naval Commander days were abundant, today's historical studies placed too much attention on the pirates. They failed to study the naval officers who fought them even though they deserved much more attention. This paper examines LI Chang-geng's life and his naval career using multiple official and civilian accounts. The official accounts include the National Palace Museum's Memorials of Jiaqing's Court（宮中檔）, Grand Council Memorial Copies （軍機處奏摺錄副）, Grand Council's Draft of Imperial Commands（上諭檔） and also the Archives of the Grand Secretariat（明清內閣大庫檔）of the Academia Sinica. The civilian authored accounts include ＂YingzhouBitan＂（瀛舟筆談）by RUAN Heng（阮亨）, ＂ShengfengDangkoJi＂（神風蕩寇記）, ＂ShengfengDangkoHouji＂（神風蕩寇後記） by JIAO Xun（焦循）, ＂YanjinshiJi＂（揅經室集）by RUAN Yuan（阮元）and recently published ＂Li Zhongyi Gong Yishi＂（李忠毅公遺詩，＂The Unpublished Poetry of LI Chang-geng＂）. His career as an officer and his relationship with the emperor are also examined. It is hoped that this paper can fill-up some gaps of the neglected field of Jiaqing Reign's naval defense.