With the rapid development of urbanization, demands of urban land increase in succession, hence, to analyze temporal
and spatial variations of urban land use becomes more and more important. In this paper, the principle of trend surface
analysis and formula of urban land sprawl index ( ULSI) are expatiated at first, and then based on land change data of
Jiayu county, the author fits quadratic trend surface by choosing urban land area as dependent variable and urbanization
and GDP as independent variables from 1996 to 2006, draws isoline of trend surface and residual values; and then urban
land sprawl indexes of towns are calculated on the basis of urban land area of 1996 and 2006 and distribution map of
ULSI is plotted. After analyzing those results, we can conclude that there is consanguineous relationship between urban
land area and urbanization, economic level etc.