This paper discusses the ongoing efforts on development of a Decentralized Data Fusion (DDF) simulator for analysis and design of a distributed fusion-based tracking system. We have identified the requirements for a DDF simulator and have developed a fully interactive, graphical user interface based scenario generation tool called SceneGen (Srimathveeravalli, Subramanian and Kesavadas 2004) for creating battlefield scenarios, and a simulation tool called VizSim for running various DDF algorithms on scenarios created in SceneGen and displaying the simulation results in an easy to understand fashion. SceneGen and VizSim has been designed with a full compliment of user utilities, including an efficient terrain database generation module, a sensor report generation module and the database connectivity to store and retrieve scenarios and simulation results. The innovative visualization techniques used in the simulator helps in displaying the data in a fashion that transfers maximum information to a user. Both SceneGen and VizSim have been tested successfully for running scenarios consisting of a large number of entities.