The judgment about the main direction of the enemy air attack is very important for operational command. This paper focuses on the need of decision-making for air defense of critical area and analyzes the nine major indicators that affect the main direction of the air-raid target. With consideration of the minimum deployment spacing between the firepower units, the gray relational clustering method is used to rationally divide the sub-directions. The Principal Component Analysis (PCA) method is used for dimensionality reduction of the impact indexes, which reduces the correlation among the indexes and the calculation cost. A comprehensive evaluation model is built to calculate the sorting of the directions.The results show that the method is correct and feasible.