Focusing on the center shift phenomenon of the coercivity curves and the exchange bias field curves, the dependences of the exchange bias on θ₀, the angle of external field orientation, in ferromagnetic/antiferromagnetic bilayers are studied in the cases that Ψ, the angle between the stress field and the easy axis, is taken as π/4 or π/2. It is shown that the analytical expression of the coercivity cannot be derived by using the Stoner-Wohlfarth model and the principle of energy minimum for the whole range of the angle θ₀. We approximate the coercivity with the switching field for the θ₀ interval at which the principle of energy minimum is not satisfied, and in this way, we got the coercivity expression in the form of piecewise function. Numerical calculations indicate that whether the center shift phenomenon of the coercivity curves and the exchange bias field curves occurs depends on the value of Ψ. While Ψ=π/4, stress results in not only the change of the strength of the effective anisotropic field but the center shift of coercivity curves and the exchange bias field curves; while Ψ=π/2, only the strength of the effective anisotropic field is influenced and no such center shift occurs. The condition in which the center shift of the coercivity curves and the exchange-bias field curves occurs is that θ^*, the angle of the effective anisotropy field to the easy axis, is not equal to zero. In addition, the results also show that the jump phenomenon can only be observed while θ^*≠0, implying that the jump phenomenon is caused by the singularity of the switching field near θ^*.