Summary: A method of measuring the similarity degree between two intuitionistic fuzzy sets is studied. A possibility degree formula for the comparison between two intuitionistic fuzzy numbers is defined, and some properties of the formula are given. On the basis of the possibility degree formula, a new similarity measure for intuitionistic fuzzy sets is presented, and then the advantages and disadvantages of the similarity measure formula are analyzed. It provides better methods to apply intuitionistic fuzzy sets to decision making, pattern recognition and medical diagnostic reasoning.