The ANSYS 8-node 3D solid element solid46 was used to simulate the T300/QY8911 composite. Then, laser dislocation speckle detection under vacuum loading was simulated, the influences of different detection parameters on the detection effect were analyzed, and an experimental verification was carried out. The results showed that the laser dislocation speckle detection of the composite material was greatly affected by the defect size, defect location, and vacuum degree. When the degree of vacuum was higher, the structural deformation was more obvious, and it was less affected by the laying mode. Therefore, it was not necessary to pay special attention to the influence of the laying mode during detection. When the LTI-6200 laser dislocation speckle detection system was employed to detect the embedded defect test block, we found that defects larger than 5 mm could be accurately detected, but the detection characteristics of deeply buried defects (below 15 layers) were no longer obvious. During the detection, it was only necessary to ensure that the vacuum degree was less than 1000 Pa, with no need to pursue a higher vacuum degree. The simulation and experimental results were basically consistent. This showed that the established model was reliable and could be used to predict the detection results, which has important guiding significance for the formulation of laser dislocation speckle detection technology for use with composite materials.