The landuse information was extracted from the remotely sensed imagery in the years of 1986

1997

and 2006

automatically.Based on the thematic maps

the quantitative change over last 20 years was analyzed.At the same time

the indexes of the relative rationality of the landuse structure

mean patch area

patch particle fraction structure

and patch area standard deviation were used to analyze and evaluate the patch changes of the cropland

grassland

and forest.Analyses indicate that (1) cropland has decreased since 1986 and the decreased range was larger during the period from 1997 to 2006.On the other hand

grassland

forest

residence

and industry increased and the change range was larger from 1997 to 2006.(2) Landuse structure was improved

but the general pattern did not change.More cropland was distributed on the slope greater than 25 degrees.(3) The cropland fragmentation was continuously rising and its distribution was more dispersed.Otherwise

the distribution of grassland was more concentrated and more continuous.The small and middle patch numbers of forest largely increased

which resulted in the more obvious difference in the patch quantity structure.