The interface characteristic influences the strength of the adhesive joints. For this reason, there have been studies to improve the strength of the adhesive joints using various surface treatment methods. One of these methods, mechanical interlocking by surface roughness, has been known as an effective method but an analysis of the roughness effect is not easy because the roughness profile such as height, shape, and density of peaks and valleys by sandblasting, sandpaper or etching is random. In this paper, micro-patterns on a bonded surface of a steel substrate were fabricated then single leg bending joints with carbon fiber reinforced polymer (CFRP) and steel were manufactured by a co-curing process. The mechanical interlocking effect was analyzed with three-point bending tests of single leg bending joints. Experimental results show that the mechanical interlocking effect leads to material damage and energy absorption, and complicated failure characteristics occur due to the micro-patterned surface. A cohesive zone model was introduced to simulate the single leg bending joints with the micro-patterned interface. A finite element analysis was performed to predict the failure load and load-displacement curve of the single leg bending joints with the micro-patterned surface and numerical results were compared with the experimental results. Failure loads obtained by the numerical results predicted the experimental ones with a relative error of 10%.