Abstract: Debris is a kind of disasters in mountainous region that can cause heavy loss. The article introduces a set of economical evaluation system by which we can caculate the damage of debris flow. The article divides the loss into direct product goods value, direct service value, indirect value, option value and existence value. The direct product goods value includes two kinds：the kind that can be recovered and that can not. The direct product goods value can be represented by all kinds of goods damaged by debris flow. The kind that can be recovered uses shadow engineering method to evaluate, the other uses market valuation method. The direct service value means the service that could be provided by the damaged goods, it must depends on certain condition. Indirect values means the service function of society and environment, we can use shadow engineering method and substitute expense method to caculate different kind. Option value is the value we can use in future, it is caculated through the concerned persons'willingness to pay. Existence value can be evaluated by convey method or personal donation and government investment, it means the value that people want to pay to make the goods exist.

Key words: debris flow, damage, economical evaluation, system method