Design of a distributed transaction processing system is a complex process. The paper describes the design and implementation of a general purpose scalable simulation environment (SimDS) for designing and evaluating the performance of distributed transaction processing systems. SimDS is a distributed simulation system where each data server is implemented as a separate process that communicates with each other through user datagram protocol. The paper describes the features of SimDS including various design policies that can be modeled by the system. It also discusses different design issues that one needs to consider in the implementation of a distributed simulation environment. The paper concludes with some test examples where SimDS was used to simulate different configurations of a real-time transaction processing system.