According to the problem of weight assignment for multi-criterion in uncertain information system, the disadvantage of the traditional analytic hierarchy process (AHP) is analyzed; the Method of weight assignment for multi-criterion based on grey interval AHP is put forward. At first, grey interval numbers are imported as a mean to deal with the evaluation information in the proposed method, the quantitative representation of uncertain information is carried out; the loss of information is decreased. Then, base on grey relation analysis and AHP, the relational degree of each criterion is calculated by using grey interval relation analysis, which reflects the relative important degree of each criterion. The judgment matrix is constructed, which fits in with consistent requirements spontaneously. The weight value of each criterion is achieved. Finally, the evaluation example proves that the proposed method is feasible.