Considering that the existing methods of evaluation of air attack threat against target is not fully ideal, a new method of evaluation of air attack threat against target based on interval numbers TOPSIS is proposed. A criterion system of evaluating air attack threat against target is founded and a standardization approach to the index value of evaluating the threat against target in the form of interval numbers is presented. The calculation steps for solving the index weight is given based on the optimization idea and using the concept of deviation degree and ideal value when the index value is an interval number and the index weight is unknown, which conquers the subjectivity of the former methods. Then the mathematical model for evaluating the threat against target by interval numbers TOPSIS is established. Finally, a numerical example of evaluating the air attack threat against target is given to show the rationality and effectiveness of the method.