This paper tells the basic concept of custom forfeit crisis and analyses the procreant reason resulting from the custom forfeit. It points out the existent problems of the traditional analysis models in evaluating custom forfeit risks. The paper puts forward a research method of custom forfeit crisis based on decision tree. An Algorithm ID3 is described at length, the concept of right entropy is put forward, and the Algorithm ID3 is improved. An analysis experiment of custom forfeit risks on decisi...