In this article, the consensus problem of leader follower nonlinear multi-agent system in directed graph with nonzero leader input is solved. By using relative output information, a distributed observer based adaptive event-triggered protocol is proposed to achieve consensus. However, many results about nonlinear multi-agent systems can only reach a bounded consensus error rather than asymptotically stable, the control protocol in this article can achieve asymptotically stable by adopting appropriate event triggering mechanisms and processing methods. Moreover, the zeno behavior will not exhibit for each agent. At last, several examples validate the efficacy of the above protocol.