Considering the electrostrictive，magnetostrictive effects in the ferroelectric （FE） phase and ferromagnetic （FM） phase and the elastic stress arising from FE/FM and film/substrate interfaces，using the Landau-Devonshire thermodynamic theory，we investigate the magnetoelectric coupling effect in epitaxial 1-3 type multiferroic nanocomposite thin films. We renormalize the dielectric and magnetic coeffcients twice and obtain the quasi-intrinsic magnetoelectric coupling in Landau free energy function of this multiferroic system. Then，the electrical-field-induced magnetization and polarization for films of different thickness in 1-3 type BaTiO3-CoFe2O4 nanocomposite system are analyzed. Our results show that the relaxation of the in-plane compressive stress of the thin film makes magnetization and polarization both decrease with the increasing film thickness，and an applied electric field can result in the reversal of magnetization in step with the switching of the electric polarization due to the out-of-plane elastic coupling between the interface of the FE and FM phases. Our results agree well with the experimental results.