C factor, known as cover and management factor in USLE, is one of the most important factors since it represents the
combined effects of plant, soil cover and management on erosion, whereas it also most easily changed variables by men
for it itself is time-variant and the uncertainty nature. So it's vital to compute C factor properly in order to model erosion
effectively. In this paper we attempt to present a new method for calculating C value using Vegetation Index (VI)
derived from multi-temporal MODIS imagery, which can estimate C factor in a more scientific way. Based on the theory
that C factor is strongly correlated with VI, the average annual C value is estimated by adding the VI value of three
growth phases within a year with different weights. Modified Fournier Index (MFI) is employed to determine the weight
of each growth phase for the vegetation growth and agricultural activities are significantly influenced by precipitation.
The C values generated by the proposed method were compared with that of other method, and the results showed that
the results of our method is highly correlated with the others. This study is helpful to extract C value from satellite data
in a scientific and efficient way, which in turn could be used to facilitate the prediction of erosion.