LiNbO3-based integrated optical waveguide Mach-Zehnder interferometer (MZI) with push-pull electrodes and evanescent field sensing window is developed. By using standard micro-opto-electro-mechanical-system (MOEMS) technique and titanium-indiffusion method, LiNbO3 monomode channel waveguide MZI array with modulating electrodes is fabricated. The near-field profile of the guided mode is detected after launching light into the LiNbO3 waveguide by fiber end-fire coupling. The phase-modulating property of the LiNbO3 MZI is investigated. The experimental results show that the phase modulation of the MZI is fully reversible and its half-wave voltage Vπ is 5.61 V, and fringe contrast is 0.62. The phase-modulating capability allows the initial phase of the MZI device to be a quadrature point to make the device work in the linear-response region for biochemical sensor.