A dynamic simulation strategy based on modular approach is presented and its implementation is described. The modular approach is very appealing to engineers, as it is easy to understand and to make use of well-established knowledge of each module. A process can be partitioned into several clusters which consist of strongly coupled units according to the process dynamics or topology. A mixed form of simultaneous and sequential simulation based on this cluster is implemented as a prototype dynamic process simulator, MOSA. Currently, ODE mode simulation for solving dynamic model equations is used because it is relatively easy to implement.