The bilayered magnetoelectric composite model has been analyzed. The non-homogeneous partial differential equation of the magnetoelectric material interacting with the microwave has been obtained in the condition that the partial derivative of the microwave is non-zero along the transmitting direction when the size of the magnetoelectric material is comparable with the wavelength. The analytic solution is solved for the equation at resonant condition, and then the analytic expressions of the magnetoelectric coefficient and the equivalent electric parameters are calculated. The results show that there is a correlative coupling term in excess in the magnetoelectric coefficient,the magnitude of which is related not only to the material parameters, but also to the microwave’s velocity in the material, and the equivalent admittance is related to the microwave’s frequency.