The flexural performance of thin high-strength concrete slabs externally reinforced with carbon fiber-reinforced polymer (CFRP) laminates at their soffit was studied in this work using a non-linear three-dimensional finite element model. A numerical model was created in this research using a nonlinear finite element software (ABAQUS) based on the results from an experimental study to validate the experimental results. For the concrete component, a concrete damage plasticity model was applied, and the traction-separation law was used for the CFRP-concrete contact. A thorough parametric study was carried out to comprehend the numerous factors affecting the CFRP reinforced slabs. Concrete's compressive strength, the usage of a transverse laminate of CFRP, various widths of FRP laminates, and the number of layers of CFRP were among the parameters considered in the study. It was found that an improvement in the capacity of the slabs occurred with the increase of compressive strength of concrete and the width of FRP layers. On the other hand, when using a transverse layer there was no effect on the capacity of the slab.