Abstract: The accuracy and scope of vegetation fraction by NDVI dimidiate pixel model was studied in this paper. Selecting the appropriate NDVIsoil and NDVIveg for urban areas, vegetation fraction values were calculated respectively based on TM of Hefei City, Anhui Province in 2002 and 2007 by NDVI dimidiate pixel model, changes in vegetation fraction were obtained by image – minus method. For Hefei City, during the study period, vegetation coverage in general decreased. The most obvious was the decline in Binhu New Area and Baohe Industrial Park, decreased values were 16.7% and 21.4%, respectively. The sharp reduction of vegetation cover caused by urban expansion is a remarkable ecological problem. Compared with the results of aerophotograph surveying, the value of vegetation fraction obtained by this method is higher in low vegetation–covered area, and which is lower in high vegetation–covered forest area, but the vegetation fraction change calculated by image –minus method can eliminate some system error and achieve higher precision in all areas, so image –minus method based on NDVI dimidiate pixel model can serve as an important means of monitoring vegetation cover.