Electric field tuning of magnetization is a viable path to realize magnetoelectric (ME) coupling effect while developing novel multifunctional devices. The combined charge and strain effects can produce multilevel manipulation in multiferroic heterostructures. Both charge and strain co-mediated ME effects were investigated in NiFe2O4/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (NFO/PMN-PT) and NFO/Pt/PMN-PT heterostructures. The charge effect was detected by the existence of magnetization imparities between the positive and negative fields. The imparities could be enlarged by inserting a Pt buffer layer between the NFO film and PMN-PT substrate. The suppressed depolarization field effect enhanced ferroelectric polarization of PMN-PT, which strengthened the polarization-dependent charge effect in the NFO/Pt/PMN-PT heterostructures. The enhancement of the charge effect helped achieve a stronger ferromagnetic-ferroelectric coupling effect.