The invention discloses a laser ultrasonic phase-locked detection system and method for a micro defect on a surface of a turbine blade. The system comprises an industrial robot, a computer control andprocessing system, a signal generator, a phase-locked amplifier, a semiconductor laser and a pulse laser. A photoacoustic probe is installed at a front end of a working arm of the industrial robot, one path of an output end of the signal generator is connected with the phase-locked amplifier, another path of the output end of the signal generator is connected with the pulse laser through a firstpower amplifier, and the pulse laser is connected with the photoacoustic probe. The semiconductor laser is connected with the photoacoustic probe through a beam splitter, and the beam splitter is connected with the phase-locked amplifier through the photoelectric detector. The system and the method disclosed by the invention have the advantages of easy operation, reliable detection result, high detection efficiency and good application prospect.