In the research of the data envelopment analysis method, when the input and output value of the decision making unit is interval number, the calculation of the relative interval efficiency depends on the choice of the front face of the production. Therefore, by the comparison of the interval model of slack based model(SBM) under different production frontier, it is concluded that it's most favorable for the decision making unit ranking by the interval efficiencies which are calculated both by the best production frontier. Then, the interval number similarity theory is introduced, and the fuzzy similarity matrix of interval efficiency is established. The reference interval efficiency unit similarity method is proposed, which is used to cluster and sort the decision making units. Finally, a numerical example is given to illustrate the feasibility and effectiveness of the proposed methods.