In this paper, the propagation characteristics of s-wave in aluminum cylinder are studied by finite element method for the detection of different Angle defects in small diameter metal cylinder. The energy range of s-wave was determined by the study of s-wave directivity, and the artificial rectangular defects with different angles were set in the main energy range of S-wave. The propagation characteristics of PRS wave (the primary reflected s-wave interacting with the defects) were studied by B-scan method. Based on the statistical study of the range of scanning Angle of PRS wave, the optimal detection Angle β (the scanning Angle with the maximum amplitude of PRS wave within the range of scanning Angle) was determined. According to the relationship between the arrival time of the largest PRS wave and the defect Angle α, the error of α Angle was 0.025 when the Angle was 30°, and the error of other defect angles was less than 0.02. This paper visualizes PRS waves at different α angles by using the range of scanning angles and the optimal detection Angle β, and proposes a method to evaluate the α Angle by extracting energy points. The above research results provide a certain degree of reference value for laser ultrasonic detection of internal defects of cylindrical materials.