Ultrasonic Nondestructive Testing (NDT) supports field use and has a strong resolution, which is a key developing method in the field of structural health supervision and testing. In recent years, contact-type technical paths such as patch detection, medium coupling detection, and air coupling detection based on piezoelectric sensors have been formed, which are widely applied to many industries. With the integration of high-quality pulsed laser technology and the research on the mechanism of laser-matter interaction, the detection technology of pulsed laser-excited ultrasound has gradually developed. This technology is expected to solve the problems of surface pollution and fixed detection area caused by traditional piezoelectric-excited adhesive sensors and coating coupling agents. The ultrasonic wave excited by pulsed laser includes longitudinal wave, transverse wave and surface wave, and its propagation velocity is related to the density and elastic constant of the material. In the past, the spot source mode and line source mode of a pulsed laser beam, as well as the line source array mode modulated by lens array and fiber bundle with fixed physical structure, limited the flexibility of spatial expansion of pulsed laser, and also restricted the development of structural response characteristics and signal-structure correlation analysis under the new excitation mode. The disadvantages of pulsed laser excitation are: the monochromatic coherence of laser restricts the modulation ability of beam spot, which leads to the limitation of ultrasonic time-frequency mode, meanwhile, the structural damage threshold limits the energy of pulsed laser, which leads to the shortage of ultrasonic signal intensity. In this paper, the spatial expansion of pulsed laser is combined with laser ultrasonic nondestructive testing technology. Then, the structural response of laser transient grating acting on aluminum alloy plate is studied from two aspects: numerical analysis and experimental research by adopting the idea of numerical analysis to reveal the law and experimental research to verify the method. By deploying observation points at different distances and directions from the center of the grid excitation, the peak gain and the decrease of energy density of the grid excitation signal are obtained for the first time, and the direction angle of near-field enhancement is revealed. The structure size of the simulation model is 50 mm×50 mm×5 mm, the number of grids is 189 062, and the number of computing nodes is 32 028. Mesh encryption is carried out near the center of the upper surface of the aluminum plate, and transition treatment is carried out in a certain range to meet the comprehensive requirements of convergence of the loading area and controllable overall calculation scale. In the field of laser processing and laser processing, aiming at the laser absorption process of rough surface, the reflection-absorption comprehensive model and lumped test method are developed to measure the laser absorption rate. In terms of numerical analysis, the influence of surface roughness on absorptivity under the framework of reflection and absorption model was studied. The excitation process of laser transient grating with a 1mm diameter, 1ns pulse width and 6 mJ single pulse input was simulated, and the comparative analysis of point laser source and line laser source with the same energy was carried out. The numerical results show that the peak value of ultrasonic signal under transient grating excitation was 2~5 times that of point source excitation when the observation distance less than or equal to 4 mm, and the surface energy density of the structure was about 1% of that excited by point source and 12.7% of that excited by line source. The principle of the experiment is that the laser beam spot generated by the pulse laser is split and interfered with by the transient grating module, then, a "bright and dark" laser transient grating is formed. The transient laser grating acts on the surface of the aluminum plate, and the ultrasonic wave is excited in the aluminum plate by thermoelastic effect, which causes the longitudinal displacement of the structural surface. The laser interferometer is used to collect the displacement of the structure surface which is 2 mm and 10 mm away from the center of grating action, and the collected signal is displayed by oscilloscope. The device includes pulse laser, transient grating module, laser interferometer, oscilloscope and aluminum alloy plate. In terms of experimental research, the transient grating module was developed, and the laser transient grating ultrasonic experiments were performed on aluminum plate. The experimental results show that the amplitude of ultrasonic was about 1 nm under 60 kHz high pass filtering, the maximum relative deviation of the surface displacement peak was 8.91%, and the deviation of surface acoustic wave velocity was 6.62%, corresponding to the signal delay at 10 mm from the center of the grating. Synthesize the above analysis, the dispersion of laser beam spot excited by laser transient grating reduces the energy density per unit area of the structure surface, and forms ultrasonic enhancement along the grating direction, which lays a good foundation for improving the signal-to-noise ratio and ensuring the safety of the structure.