Abstract: The qualitative descriptions of the area rule bring some confusion and problems to the actual aircraft design work. The linear perturbation assumption in conventional theoretical derivations does not suit the development for more and more refined aerodynamic design in the future. For AGARD-B standard model which has typical shape characteristics of high speed aircraft, we combined the CFD with optimization methods to probe the body modification form for optimal drag reduction. From that, a better drag reduction result and more detailed modification principles of drag reduction are obtained compared to those obtained from the traditional area rule method. Based on the present principles, through the analysis of drag force felt by each component and comparison of the drag forces on the body surface before and after modification, it is found that the essence of area rule drag reduction is the advantageous interference produced among the adjacent components of the aircraft configuration. Finally, the drag reduction effects of fuselage shrinkage cross-sectional shape are studied and verified. The comparison among different lift coefficient conditions validates that the drag reduction effect of area rule is the same under various lift coefficients and angles of attack condition.