Abstract: The conception of tourist background trend line is put forward in this paper. Based on the statistic data of tourists from abroad from 1978 to 1996, by inner insertion method and eliminated the major interference, 4 tourist background trend lines were founded by optimization simulated method. They are tourists from foreign countries, tourists from Hongkang, Macao and Taiwan, tourists who are overseas Chinese and total number of above three. Two scientific functions of tourist background trend ine are discovered: (1) Compared with statistic line, it indicates the rise and fall of tourism just as tourism barometer. (2) The extension of the line can predict the future. As applications, this paper with two functions above, explained the concave curve induced in 89’s politic wave and forecasts the next 4-year development trends of tourists from abroad in China.