The traditional method is not adaptable for threat assessment of beyond-visual-range multi-target combat of the fourth generation fighter, thus we proposed a new threat assessment method.Based on the traditional multi-target threat assessment method, the new method took combat height and stealth performance of the fourth generation fighter into account, calculated out the objective weight and subjective weight of threat assessment index respectively by fuzzy optimal method and IAHP, and finally gained the comprehensive weight.The improved TOPSIS was used for the multi-target threat assessment.An application example is given and the results show that the method is reasonable, effective, and suitable for the threat assessment of beyond-visual-range multi-target combat of the fourth generation fighter.