自鴉片戰爭以來，中外關係的運作大抵建立在不同階段的條約關係上，學者亦有稱之為「條約體系」(Treaty System)。然而不同階段的條約對美國在華商務發展究竟產生那些影響，或者說條約關係在實際的商務交涉中具有怎樣的功能，乃至於條約關係的實際運作在個別的商務個案呈現怎樣的形貌？過去有關條約關係的研究角度較偏重政治外交層面，而較少從中外經貿關係和條約內容的運作來考察其意義。本文主要以個案來呈現條約關係如何落實於近代中美經貿發展關係中，藉此釐清條約利益在商務發展中的實質面向。本文探討二件案例：一、從「有領事方准通商」至「領事不得兼任商人」的規範和爭議：早期美國駐外領事的奉派，往往商業功能大於政治意味，由於美國在海外拓展的起步較晚，領事制度不及歐陸國家；更與在中國最大利益的英國駐華領事制度殊為不同，係清末中美關係中值得注意的現象。二、1882年韋特摩耳(W. S. Wetmore)意圖於上海設置紡織公司案的爭議：根據中美相關條約的規定外人可否在通商口岸設置工廠，引起中美雙方對於條約的不同解釋和爭辯。考察此二個個案，有助於釐清條約關係在清末中美經貿外交中的適用程度，以及美國在華商業利益的具體面貌。

Chinese-Foreign relationship was based on specific treaties of different periods since the Opium war, which was described by some historians as “Treaty system”. While the Treaty-System in different periods had different effects in different cases, what was the real relationship between American business and its treaty interests in China? What kind of effect did the treaty system has in U.S. China trade? This article tries to explore how the U.S. treaty interests affected American business in China by case study. The article is focused on two business cases. One is American consular service in China. American consular took more responsibility in opening the market than political mission. As the later comer in China, American consular system was not perfect and quite different from Britain one. Another case is the dispute about a plan to build a textile factory by W. S. Wetmore in 1882. In these two cases, Chinese and American defended their positions according to the same Treaty, but with different explanation. It will illustrate the application of Treaty System in Late Ch'ing and help understand the real situation of American business in China by examining these two cases.