In the recent past, wireless sensor networks have been introduced to use in many applications. To design the networks, the factors needed to be considered are the coverage area, mobility, power consumption, communication capabilities etc. The challenging goal of our project is to create a simulator to support the wireless sensor network simulation. The network simulator (NS-2) which supports both wire and wireless networks is implemented to be used with the wireless sensor network. This implementation adds the sensor network classes which are environment, sensor agent and sensor application classes and modifies the existing classes of wireless network in NS- 2. This NS-2 based simulator is used to test routing protocols – Destination-Sequenced Distance Vector (DSDV), and Ad-Hoc On-Demand Distance Vector (AODV) as one part of simulations. Finally, the sensor network application models and the extension methods of this NS-2 based simulator for simulations in specific wireless sensor network applications are proposed.