With recent improvement in adhesive performance, adhesive joints are used more in various industrial fields. Despite their advantage in connecting dissimilar adherends, adhesive joints are considered not suitable for key components of mechanical structures due to their large scatter in joint strengths. There are many factors that affect the strength of adhesive joint. However, the general bonding factors are (1) mechanical bond, (2) physical bonding, (3) chemical bonding. The adhesion mechanism is complex because these theories occur at same time. Thus, it is necessary to consider the factors separately. And it is important to understand the bonding mechanism on interfaces in adhesive joint and to improve the reliability of the joint strength more. In this study, the tensile strength of single lap joint was measured in order to investigate the influence of various surface treatments and strength characterization of adhesive. Specimens consist of aluminum alloy plates (A6061). Large-area electron beam (EB) and plasma were used for surface treatment. Each one of specimens were examined from the view of wettability, roughness parameter. Compared with unirradiated specimens, other joints improved the wettability and tensile strength. The inference of large-area EB irradiation on adhesive mechanism was discussed.