A model is developed for the effects of surface stress on low-frequency magnetoelectric (ME) effects in flexural magnetostrictive-piezoelectric bilayers, and we further take cobalt ferrite and lead zirconate titanate (PZT) as a specific case. The results show that flexural deformation can suppress the ME voltage coefficient, especially for moderate PZT volume fraction. Owing to residual surface tension, the ME voltage coefficient should depend on magnetic field, and this tendency is weakened with increasing magnetic field. Interestingly, the size dependence of ME voltage coefficient is found when the thickness of bilayer reduces to nanoscale.