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Testing of the ultrasonic signal is an important matter in laser ultrasonic field. Because of the weakness of the surface vibration caused by ultrasonic, common methods can hardly satisfy the industry application commands. In this paper, a noncontact method, based on two-wave-mixing and the optical adaptivity of photorefractive crystals, is presented to detect the ultrasonic signal on a rough surface. The photorefractive effect and two-wave-mixing characteristics of photorefractive crystals are introduced, followed by the design of ultrasonic signal testing system using a photorefractive crystal, including the stray light collection, crystal protection from high voltage and noise suppression of optical maser. Finally, experiments are carried out to verify the performance of the system. The results show the ability of the system in ultrasonic vibration detection on a few? kinds of rough surfaces and material defect evaluation.