Abstract: A method based on classification tree with attributes is presented in this paper, to calculate the similarity without engineering parameters between different process plant equipments. In this method, it is needed to firstly build a classification tree that can meet the completeness requirements defined below and map the equipment to tree node. Then, min-distance, information granularity and smooth ratio of set to union of attribute descriptions are involved in the calculation. The result shows that it has good mathematical properties and can be physically explained well, it also shows that the method performs well when applied to practice.