Abstract: In this paper the concept of blind information is introduced,the blind information in dam safety comprehensive assessment is analyzed. Based on introducing the definition of blind data, the process method of blind information is applied to the practice on dam comprehensive assessment. With the observation items in Xiaolangdi Project,combined with the operation principles used, the blind data of several types of influencing factors determining the assessment result are averaged and the scientific and reasonable assessment result is acquired. It is verified that the blind data have good values in dam safety comprehensive assessment.