In this paper, we try to apply the economic model of economic growth and trade expansion (in the case of large country) to the economic analysis of regional economic difference in order to research the expansion course of regional economic difference At first, we introduce the economic model of economic growth and trade expansion (in the case of large country) briefly Secondly, we apply the economic model of economic growth and trade expansion (in the case of large country) to the regional economic analysis to set up the regional model of economic growth and trade expansion and use this model to research regional economic difference We find that the welfare of some regions begin to decrease correlatively due to economic growth and trade expansion in the regional labor division Thus we draw a conclusion that it is the term of trade that leads the regional economic difference to expand Thirdly, we inspect the conclusion with the figures of east and west of China Moreover we inspect the causal relationship between the term of trade and the regional economic difference through hypothesis testing of Granger causality and find out that there exists some causal relationship between the term of trade and the regional difference At last, we draw some conclusions as follows: (1) In the regional labor division, some regions are inevitably in a unfavorable state With economic growth and trade expansion, their terms of trade degenerate and welfare begin to decrease correlatively which led to expansion of regional economic difference (2) By inspection of the west and east of China, we find that there is causal relationship between the term of trade and regional economic difference (3) With the study of regional economic difference, we draw a conclusion that demand change is the main cause of degeneration of the term of trade Because the demand is in the base of industrial structure, so our study supports the conclusion that changes of industrial structure are the main impetus of regional economic growth