The circular ablation spot is axisymmetric and easy to obtain,so it has a wide range of applications in laser ultrasonic inspection.In order to gain the corresponding characteristics of longitudinal wave sound field,an excitation source model is established.The amplitude distribution of sound pressure on the acoustic axis in the near field is discussed and the near field length is calculated.Using the area integral,the expression of the sound pressure amplitude in the far field is derived,and the sound field energy is simulated.Through analysis,it is found that the longitudinal wave energy is symmetrically distributed about the axis of the acoustic beam and reaches the maximum value on the axis.In addition,the spot size directly affects the directivity of the longitudinal wave sound field.A laser ultrasonic non-contact measurement system is set up.The signal amplitude is corrected according to the propagation distance,based on the reciprocity principle,directional experimental data is obtained and the theoretical analysis results are verified.