The Y-waveguide electro-optical response test instrument can measure the half-wave voltage and waveform slope parameters of Y-waveguide integrated optical phase modulator with high precision and high stability. The test instrument adopts high stability broad spectrum light source, wide bandwidth modulation driving circuit, high-speed closed-loop control strategy and fuzzy algorithm for feature extraction, with self-adaptation of the insertion loss of Y-waveguide device and self-tracking function of the intrinsic frequency of the optical path, which can realize the Y-waveguide electro-optical parameters of high efficiency, accuracy and stability of the one-button full-automatic measurement.