This brief focuses on cooperative output regulation (COR) problem for linear multiagent systems (MASs) under the directed topology. The fully distributed event-triggered control protocol is designed to solve COR problem. In order to reduce the communication frequency, the dynamic event-triggered mechanism is proposed by introducing positive internal variable. One main advantage is that the method inherits the advantages of event-triggered control and adaptive control to deal with the COR problem, and does not depend on global information. At last, a numerical example is given in the supplementary material to verify the validity of the obtained results.