Since Open and Reform,the enlarging regional economic disparity in China aroused much attention.This paper uses Shorrock's method to decompose the effect of foreign trade on the widening of regional economic gap.The conclusion is that from 1978 to 2005,the contribution rate of foreign trade to the increasing regional economic disparity is 33.77 percent.After that,this paper pointes out the me chanism through which foreign trade can work on the regional economic growth disparity.They are multiplier mechanism,technology transfer mechanism,agglomeration mechanism and competition mechanism.At last,this paper holds that reducing the regional disparity on foreign trade development can do well to the decline of regional economic growth disparity thus boost the harmonious growth among regions.