This paper studies the leader-follower synchronous of multiagent systems (MASs) over finite fields by the event-triggered control (ETC). Firstly, the MASs over finite fields with ETC are modeled as algebraic form by the semi-tensor product (STP) method, based on which, the event-triggered synchronous problem is transformed into the set stabilization problem about the system with algebraic form. Secondly, the maximum invariant set is selected as the target set to reduce the number of controller execution times. Thirdly, the necessary and sufficient conditions of the event-triggered synchronous of the MAS as well as the design method of the optimal state feedback event-triggered controller are given. Finally, an example is presented to illustrate the conclusion of this paper.