Under the background of deepening economic globalization and constant changes in international division of labor, internal mechanism of international inequality issue has new changes and Marx's classical inequality theory is facing a novel challenge. Based on the new form of international division of labor, this paper puts the inequality in three fields of international trade, international investment and international finance into a unified "integration" framework, analyzes how international inequality transforms from inequality in a single field to integrated inequality in many fields, proposes the concept of international inequality integration, and further constructs a mathematical model of international trade interests inequality integration. Theoretical model shows that the inequality in an international economic field is integrated with inequality in other international forms, and is embodied in the increase or reduction in the transfer of international surplus value in an international economic field owing to the integration of other international economic activities in terms of quantity. Based on theoretical analysis above, this paper takes the international trade inequality as an example, and explores the problem of inequality integration in the three international economic fields. It comes to the results as follows:firstly, international investment inequality and relative differences in real effective exchange rates have a significant positive impact on international trade inequality; secondly, there does exist long-term bidirectional causality in inequality between international trade, international investment and international finance, namely there is an integration among these three. Therefore, the governments should examine different international economic fields on the same platform and reduce international inequality in a field accompanied by policy formulation in other two relative fields, to achieve a multiplier effect.