In this paper, we study the synchronization control problem for a class of discrete-time complex dynamical networks (CDNs) under an event-triggered mechanism (ETM). First, a discrete-time distributed periodic ETM is developed based on communication measurement. Under this mechanism, the signal is sampled in a periodic manner, but whether the control signal is updated or not depends on the pre-designed triggering condition. The sampling signal is designed as the communication measurement calculated by both state feedback and inner communication among nodes. Compared with the existing discrete-time ETMs, this method considers the topology connection among network nodes and avoids the continuous measurement of signals. Therefore, this mechanism effectively saves communication resources and reduces the waste of computing resources. Second, in order to analyze the serrated constraint caused by the periodic sampling error, a piecewise Lyapunov function is constructed. Third, under the distributed periodic ETM, sufficient conditions are derived for bounded synchronization of discrete-time CDNs with time-varying delay. Finally, a simulation example verifies the effectiveness and accuracy of the conclusion.