For the BaTiO3 crystal thin-film waveguides, a new electro-optic (EO) modulating scheme of a two-dimensional (2D) matching method between the optical field of the lightwave working signal and the electric field of the microwave driving signal is investigated with an embedded device regime. In this 2D matching method, the two central parameters for determining the optical refractive index modulation (RIM) efficiency are (i) the overlap integral between optic and electric fields and (ii) the electric-field strength of the modulating signal, both of which are dependent of the allowable electrode gap. As a result, the higher the electric-field strength is created by the imposed drive voltage crossing the electrode gap, the higher an overlap integral is reached, and consequently, at the smallest allowable electrode gap of 4.5 μm, the usual maximum 65% overlap integral of the traditional co-planar waveguide (CPW) regime based one-dimensional (1D) matching method has been improved to 88%. Thus, for a given BaTiO3 crystal thin-film having EO coefficient r51 = 500 pm/V, when the birefringence values are −0.001 and −0.005, with the CPW device regime, the optical RIM efficiencies are 4.88 × 10−4/V and 1.83 × 10−4/V, respectively, while with the embedded regime based 2D EO matching scheme, the RIM efficiencies are improved to 8.84 × 10−4/V and 3.31 × 10−4/V, respectively, leading to the modulation efficiency improvement of 81% for any birefringence.