More and more agricultural soils have been alienated as a result of rapid urbanization in the Yangtze Delta. With the aid of the nested subset method, RS and GIS technologies tools and the TM images ofthe years of 1984, 1995, 2000 and 2003, expansion of Nanjing city was analyzed in the past 20 years. Results showed that the degree of fill of the land calculated with a professional software tool (Nested Temperature Calculator Version Nov 1998) has been doubled (from 3.5% in 1984 to 7.2% in 2003), forming a nested pattern, higher and higher in degree; Geographical variation Call be found of the fill values of different towns. Some towns or districts showed very clear increase in the fill due to the more rapid growing urbanization while some others did less.