This paper investigates the methods to calculate airfoil drag including the method of airfoil surface integration of pressure and shear stress and the method of integration of momentum loss in a wake cross section. The flow field solution is provided by the numerical simulation of the flow around the airfoil flying in the atmosphere or the airfoil installed in the wind tunnel test section. The drag coefficients obtained by the two methods are compared and those obtained by integrating in different wake cross sections are also compared. The optimal cross sections are found for wake loss integration to obtain drag both in the free flight case and the wind tunnel test case, i.e., the optimal position to install wake rake is obtained.