Three series of steel-plate single-strap joints bonded by Carbon-Fibre Reinforced Polymer (CFRP) sheets, which are used with an adhesive material, are investigated in this study. Experimental and finite element (FE) analyses using ABAQUS software are employed for this purpose. The main objective of this study is to provide further understanding of the bonding mechanism of strengthened single-strap joints under a pure-tension load. The experimental tests specifically investigated the effects of using multiple CFRP layers with normal/high steel surface roughness on the bonding failure mode, bond-load capacity, and effective bond length. Furthermore, the FE analysis was used to establish the shear stress-slip relationships of the suggested specimens. The results showed that the bond capacity (ultimate bond load) of single-strap joint did not increased much when the CFRP bonding length pass the effective bond length (limit). The bonding capacity (ultimate bond load) of single-strap joint increased only of about 14% when increase d the CFRP layers from two to four. Moreover, the behaviour of the shear stress-slip relationship was not significantly affected by increasing the number of CFRP layers.