Abstract: Decision tree analysis,Mahalanobis distance discriminant analysis and Fisher discriminant analysis were employed to classify ecological hazards of 61 chemicals.Comparison between these methods showed 92%,87% and 75%,respectively in correctness of the classification.Decision tree was not only the highest in correctness,but also reduced 2 indexes in the evaluation.Moreover,analyses of the 61-index matrix demonstrated that the classification capacity of the decision tree method was very stable and its correctness displayed normal distribution,which remained around 92%.So it is the optimal method for the classification of ecological hazard in these methods.