At present, the feasibility of the emergency preparation plan (EPP) for dam reservoirs is uncertain; and the appraisal technology of EPP feasibility is still inadequate, which leads to difficult supervision of EPP making and in some extent affects the EPP making and relevant enforcement work. In the researches on EPP appraisal methods which have been studied by other experts and scholars, EPP feasibility appears to have a notable characteristic that comes from index incompleteness. This incompleteness can affect the implement results of EPP feasibility appraisal. In order to reduce the effects given by the index incompleteness, it is necessary for us to carry out studies of new appraisal methods for EPP feasibility. Based on the existing research findings of reservoir EPP feasibility evaluation methods, considering a gray feature in the feasibility evaluation system with the index incompleteness, a new evaluation method is established based on a grey correlation degree, and its availability is verified through the simulation of case histories. This method is used to improve reservoir EPP feasibility evaluation technology and reduce the impact extents for the evaluation results considering the incompleteness of the feasibility index system.