In order to overcome the numerical instability problem of LBM (Lattice Boltzmann Method) in high Reynolds number scenarios, The LBM-based TF-Lattice software used in this paper adopts the hybrid-recursive-regularized (HRR) model for the LBM collision operator and the WALE model for turbulence modelling. We firstly performed a fluid dynamics simulation of the Ahmed model with different back inclinations (0°-35°) using the TF-Lattice software. The calculated results are generally consistent with the experimental and simulation results in the literature, and the errors of the drag coefficients compared with experimental data under all conditions are within 5%. A non-watertight Ahmed body is adopted to examine the influence of geometrical defects on the aerodynamic drag. The Ahmed body, a standard automotive test model, is widely used in wind tunnel experiments to study vehicle aerodynamics. However, in real-world applications, vehicles often exhibit deviations from the ideal geometry due to manufacturing tolerances, wear, and other factors. The aim of this study is to quantify the impact of such geometrical defects on the aerodynamic drag. The research employs the lattice Boltzmann method (LBM) software to analyze the flow field around the Ahmed body with and without the introduction of geometrical defects. These defects are modeled as small holes in the shape of the body. The simulations are performed under the varying location and size of the holes to explore the aerodynamics phenomena. The results indicate that the location and size of geometrical defects can significantly alter the aerodynamic drag of the Ahmed body. The holes located at the rear of the Ahmed body rarely effect the aerodynamic drag. The holes at the top or bottom are found to have the most pronounced effect. The study also reveals that the influence of defects varies with their size, with large areas leading to more substantial changes in the aerodynamic drag. The results demonstrate that non-watertight geometry with small defects can be used to produce a reasonable drag coefficient compared to the results of watertight geometry.