In this study, three Landsat ETM images obtained at different period of the growth of seed rape and winter wheat are used in a study of analyzing the potential of multi-date ETM in crop discrimination for an area near Kaifeng city in Henan province, China. We compared the spectrum development between winter wheat and seed rape before, during and after the flowering stage of seed rape. Then, we provide two different classification schemas to discriminate the two crops depend on different image combination. The first one using images between the jointing stage and flowering stage of seed rape, the other one using images between the jointing stage and leguminous stage. At last, we selected two ETM images, on March 8 2001 and April 1 in 2001, to build a decision tree to discriminate seed rape and winter wheat. And the result was compared with that from IKONOS image classification and proved that the discrimination accuracy was 87% high. And the results also told us that discrimination errors were happened in two kinds of regions. One is the regions that crop growing status were very poor, another is that the planting patches were very thin or small