This paper is aimed at soil mapping technics with remote sensing data to produce a soil map at a prefectural level （1:200000） from county level （1:50000）. The principles of mapping synthesis for our research are 1. the new boundary is delineated on the base of soil family boundary on the original soil maps

2. the regularity of soil distribution has to be studied so that soil mapping units are merged and distinguished according to the regularity and the interpretation of Landsat image

3. some mapping units with regularity are presented as association after they are merged.The mapping scale was reduced from 1:50000 to 1:200000 after the mapping units were changed from the series on original soil maps to the families on the new map. To meet the need of the scale change

some modifications for the classification system were made. The base map was prepared from topography maps which can satisfactorily reach mapping accuracy. New soil map and Landsat image were overlapped

on which the synthesis and corrections were carried out. We merged some families into one family according to Landsat image pattern and ground truth data. For same soil types without special interpretation character

we made few changes. The results show that this method is more effective than the traditional one. It saves time and expense.