Facing with the subjectivities and complexities problem to judging air-attack direction in the process of command of air defense, the paper considers many factors that affect the judgment of main air-attack direction. The paper uses the principal component analysis (PCA) to analyze and extract the factors influencing the choice of hostile main attacking direction, then realize the attack direction differentiation, calculating the comprehensive evaluated values for various different attacking directions based on integrated evaluation models of the PCA. The method provides a new idea and a new way of quantitative analysis for the differentiation, and reduces the interference of the subjective factors in the traditional methods. Through instance operation, this method can reduce the interference of subjective factors in the traditional method, and improve the efficiency and accuracy of main direction determination.