Currently, the permanent magnet generators find wide application in the renewable energies field such as the conversion of the wind energy or the tidal energy to an electrical energy. The main objective of this work is the calculation of the magnetic field created by the permanent magnets of the both selected rotor types (magnets on surface and inset type magnets) by taking into account the rotation of the rotor, and therefore the calculation of the electric field induced in the stator, which allows us to calculate the electromotive force exerted on the conductors of the stator coils in order to know the induced voltage by each generator, then, we make a comparison between them to determine the type of generator most answered in the industry. To reach our goal we use the finite elements method to solve the partial derivative equations those describe this physics problem.