Abstract: The listing of stressed plants checklist and di-vision of conservation sequence is one of the most important issues in plant diversity conservation .In this paper,the evalua-tion and gradation indexes for rare and endangered plants were studied,the method of expert system was introduced and an expert system for evaluating and grading rare and endangeredplants was established.The established expert system can,to acertain extent,simulate human experts’ thinking process .It will be helpful to turn the qualitative division into a combina-tion of qualilative and quantitative division for prior conserva-tion class of stressed plants.so as to make more objective andaccurate evaluation of the extent of stressed plant species andreasonable determination of the conservation level of plant species.