Using a method based on the system energy described by Smith and Beljers, the ferromagnetic resonance in ferromagnetic (FM)/Antiferromagnetic (AFM) bilayers under the stress field is studied. The thin FM film is taken to be a single crystal with cubic and uniaxial magnetocrystalline anisotropies, while the thickness of AFM layer is thin enough for its energy to be neglected. Numerical calculations show that the stress field will affect resonance curve only under weak magnetic field, and the critical field strength which distinguishes the weak from the strong external field depends on the direction of the stress field only.