The low-velocity impact of adhesive-bonded single-lap composite joints has been studied using a spring-mass model. In this quasi-static model, the impact response is represented by a time-dependent force, and the target joint is represented by an equivalent mass with equivalent stiffness. An analytical model has been developed to determine the equivalent mass and stiffness of the joint. The laminated anisotropic plate theory was used in the derivation of the governing equations of the two bonded laminates. The entire coupled system, as well as the assumed peel stress, were solved using both the joint kinematics and suitable boundary conditions. With the combination of a spring-mass equilibrium system and the developed joint model, a relationship between the impact force and the duration has been established. Adhesive stresses, which are believed to be the cause of failure, were predicted from the impact force. Impact tests of single-lap composite joints with different sample thicknesses and overlay lengths have been conducted to verify the proposed model.