This paper studies the adaptive control problem for unknown time-varying high-order nonlinear multiagent systems (MASs) with directed topology. A novel low-complexity distributed adaptive backstepping controller is developed to achieve the asymptotic synchronization. The designed controller regards the unknown system non-linearities as “disturbance-like” terms, which are guaranteed to be bounded by using the barrier functions, such that detail models of system nonlinearities are released. Then, the “disturbance-like” terms are compensated adaptively by designing the novel compensator at each step, such that the synchronization error is eliminated to zero eventually for each agent. In addition, unlike the existing backstepping-like synchronization approaches for high-order nonlinear MASs, the “explosion of complexity” issue is avoided without extra low-pass filters. Some simulations are shown to demonstrate the effectiveness and advantages of the developed method.