We propose a novel Z-cut lithium niobate electro-optic modulator based on a Si2N2O substrate. The structure is analyzed using the finite element method. The novel modulator with 3-dB optical bandwidth, half-wave voltage, and characteristic impedance at 1.5-µm wavelength are 120 GHz, 3.5 V and 50.2Ω, respectively. The simulation results show that the modulator can achieve wide bandwidth, low half-wave voltage, and a good impedance match. The modulator has good potential for high-speed optical transmission systems.