The tensile performance of the adhesive-bonded single-lap composite joints is studied by the finite element modeling. The effect of the lap length on the tensile properties is analyzed with respect to the stress distribution and the failure mode. It is shown that: when the lap length changes from 5mm to 45mm, the minimum shear stress gradually decreases; when the lap length is greater than 20mm, the effect of the lap length on the stress distribution is decreased; the failure load increases gradually with the lap length; the increase rate is reduced when the lap length is greater than 20mm; the failure mode of a single lap joint is to start from the edge of the adhesive -composite interface, and then the adhesive damage. The lap length affects the damage level.