本文旨在討論日本首要航業日本郵船，於20世紀初進入中國長江航運市場的過程。本文挑戰現有對日本郵船收購英商麥邊洋行的個案研究，在首次使用的日本外務省檔案中，發現日本政府介入協助日本航運擴張的新證據；同時經由閱覽大量英國外交檔案及商船公司內部文獻，本研究歸結，面對日本郵船競爭的英國航商，為了保全己身利益，遊說英國政府施行保護主義貿易政策。故本個案是對日本帝國主義擴張的研究，也是英國自由貿易政策沒落的記錄。 This paper addresses the research on the business history of the Anglo-Japanese rivalry. The NYK, a Japanese company and a newcomer to the Chinese waters in the early twentieth century, had challenged the ascendancy of the British shipping companies on the Yangtze. This paper also discusses the effects of the political support for both the Japanese and British companies. The Japanese shipping industry, backed by the Japanese Government, expanded their forces on the Yangtze by purchasing British property. The British shipping companies, with their own political support, initially overlooked the Japanese threats. However, later the British companies used British law to secure their own interests as the Japanese Government used diplomatic influence as a method of assisting Japanese business interests abroad. To conclude, this paper emphasises the critical role of political support in promoting the NYK expansion in this case study, which leads to a revision of the conclusions of some earlier research. This paper is also a survey on the Japanese imperialism, as well as a record of the decline of the British free trade policy in the early twentieth century.