A stability problem under event-triggered control for discrete linear systems with random time delays is considered in this paper. First, this paper improves an accumulative error-based event-triggered approach, which can switch the event-triggered parameter between the two-modes over time. Second, a new closed-loop discrete Markov switching system equation is derived by decoupling the accumulative error term, and the time delays are equal to the current Markov modes when the event-triggered scheme is met. Third, the co-designing problems for control gains and event-triggered parameters in the system are solved. Finally, the stochastic stability of the system is guaranteed through random analysis techniques and a free-weighting matrix method, and the effectiveness of the approach is demonstrated by using numerical examples.