In this paper, we present thread-based optimistic distributed timed cosimulation methods which reduce the overhead of optimistic simulation. First, we present thread simulation model to facilitate efficient distributed cosimulation. To reduce the overhead of optimistic simultion, we focus on the reduction of state saving overhead. Based on the thread simulation model, we perform thread-level state saving without saving the whole state of processor at each checkpoint. Especially, single checkpoint property based on the proposed thread model minimizes the number of state savings for HW threads. We give preliminary experimental results to show the efficiency of the proposed methods.