In this paper, a visualization system was proposed based on ultrasound excitation from a Q-switched pulsed YAG laser. The ultrasonic wave was received by a piezoelectric transducer. The electrical time-domain signal was analyzed in the Fourier-domain in order to detect a hole-like reflector in an austenitic stainless steel specimen. At a given receiver position, a piezoelectric transducer received the ultrasonic wave signal. The electrical time-domain signal was analyzed in the Fourier-domain. The experimental research on the influence of the relative position distance between the laser excitation spot and the defect of the test specimen was conducted. The experimental results showed a significant geometrical imaging of the reflector shape with the scanned data. Therefore, a quantitative laser ultrasound visualization system was realized along with the spectral analysis. It will provide a new method of defects detection and sizing.