The invention discloses a monolithic integrated optical accelerometer based on phase detection. The monolithic integrated optical accelerometer comprises a wide-spectrum light source, a spot size converter, a photoelectric detector, a one-way isolator, 2:1 and 1:2 type Y waveguides, a spring vibrator structure, upper, middle and lower electrodes, a waveguide reflector, a lithium niobate single crystal film layer, a silicon dioxide buffer layer, a silicon substrate, a refrigerating piece, a magnetic force feedback module and a packaged shell; the spring vibrator structure is located between thetwo branch ends of the 1:2 type Y waveguide; the upper electrode and the lower electrode are located on the outer sides of the two branches of the 1:2 type Y waveguide; the middle electrode is located on the upper surface of a mass block of the spring vibrator structure; light is coupled into the 2:1 type Y waveguide through the spot size converter and then enters the 1:2 type Y waveguide throughthe one-way isolator to realize light splitting; and two beams of the light are reflected by the waveguide reflector, are coupled into the branches of the 2:1 type Y waveguide and then are directly coupled into the photoelectric detector. The monolithic integrated optical accelerometer disclosed by the invention is high in detection precision, small in size, simple in preparation process and highin reliability and environmental adaptability.