This paper investigates the effects of the Foreign Service as an important determinant among the top five export countries, such as United States, Germany, Japan, Netherland and Republic of Korea. Foreign services are widely known as a communication channel in foreign affairs. Some recent studies have argued that foreign services might help promote trade, but they lack applicability and reliability. This paper seeks to prove that foreign services can serve as an expanded determinant of trade flows by showing that in the sixth year after the establishment of a diplomatic mission, the trade will bring about maximum returns. Both the Trade Index and Gravity Model have a long history and are widely used as methods to study trade flows. However, these two methods have shortcomings. For instance, Trade Index is a ratio, which uses real trade volume and is based on trade theory to measure the structure of trade, but it cannot forecast expected trade. The Gravity Model, as a research tool, is used by many economists. Depending on different determinants, the gravity model could be extended, and could predict expected trade flows. However, some economists argue that the gravity model lacks a foundation in trade theory. Based on that background, this paper developed a new model named the ‘integrated gravity model.’ This model is derived from the basic gravity model, but has a theoretical foundation in trade theory. Therefore, this integrated gravity model involves determinants of the gravity model and trade theory that could explain trade flows, such as comparative advantage, trade intensities and socio-economic variables. The model will extend the explanation scope and could affect trade flows to a certain extent. The Republic of Korea (RoK) is an export-oriented country and the trade flows are dynamic and occupy an important role in her economy. Therefore, this paper focuses on exploring the influence of foreign services on trade flows in the RoK. Foreign Services could promote trade by 22.2% in the RoK case, much higher than Rose’s (2005) 6% to 10%. The foreign services had large positive effects on promoting trade flows in the RoK. The foreign policy strategy may vary from country to country. Using the RoK case, we could predict that foreign services promote trade development among developing countries, especially export-oriented ones. As will be discussed, these values have important implications in trade policies. In the threshold model, we investigated the influence of an embassy on trade flows through official development assistance by looking at when embassies were established. We found that maximum trade flow happened 5 years after the exporter established its embassy in the importing country which means that in the fifth year, the government’s diplomatic relations and non-governmental communications will reach their highest point, thus their relations as well as exchange activities will be strengthened through the ODA. Based on the above discussion, as a new determinant of trade flows, foreign services have a positive effect on promoting trade flows, while after five years of establishing an embassy in the host country, the bilateral trade between the home country and host will reach its highest point. This result has a great potential and will bring a bright future to governments making investment strategies in host countries. Meanwhile, the determinants of trade flows in the new trade environment should be reconsidered in the academic field.