Scalability is very important for parallel and distributed simulations. Several techniques have been proposed to develop scalable synchronization strategies, communication services or fundamental algorithms, while little has been seen to deal with the modeling stage of the application. Learning from the HPC (High Performance Computing) lesson, it is clear that the time spent in developing a simulation application must be considered in evaluating the scalability of the application. There are many discrete event simulation platforms built for large parallel and distributed simulations, such as SPEEDES (Synchronous Parallel Environment for Emulation and Discrete Event Simulation), GTW (Georgia tech Time Warp), and YHSUPE, etc. They take Event-Scheduling as their modeling paradigm and have achieved great runtime performance, but lack in providing efficient modeling methods. To deal with this issue, a component-based specification, which can support hierarchical decomposition of large models and facilitate model reuse, is presented. This paper extends the DEVS (Discrete Event simulation specification) and proposes a component-based formalism, called EDEVS (Event-Scheduling Discrete Event simulation Specification) for the existing Event-Scheduling parallel and distributed simulation platforms.