This paper researches on sampled-data consensus of first-order delayed multi-agent systems with weighted average predication. First, the paper obtains a consensus protocol based on sampled-data by using the delay decomposition technique, and simultaneously obtains the necessary and sufficient conditions about the sampling period guaranteeing the achievement of consensus by using the stability theory of linear systems and the algebra graph theory. Last, the paper demonstrates the effectiveness of the theoretical results by simulation, obtains the sampling period, and simulates and verifies two kinds of conditions. This provides a feasible solution for the consistency problem of the sampled data control of a first-order multi-agent system.