An experimental platform of laser ultrasonic is built based on the thermoelastic effect and the laser interference reception method. The directivity of transverse waves generated by the incident laser and the effects of the inner surface defect on the ultrasonic signal are observed. According to the B-scan image, the defect location at the inner surface threaded part is detected. The experimental results show that the transverse wave with the largest power generated by the laser point source is in the direction of normal angle of 32.1°, which is consistent with the result of the theoretical analysis. The B-scan image combined with the peak-angle variation of the signal is used to locate the inner surface defect and to measure the defect width. This study can provide an experimental basis for industry application and popularization of laser ultrasonic.