Some simulators were designed for wireless sensor networks. The main goal of these simulators is to provide a framework to closely model and simulate various sensor networks scenarios. Two important factors for accurate evaluation are simulator and method of simulation. In this paper, we don’t want to produce a new simulator for sensor networks. We will show how to use current simulators for getting accurate results. On the other hand, we will talk about the role of evaluation methods in simulation results and show current evaluation method; analysis of routing protocols based on results of finite states of network, isn’t an exact evaluation for using in a special application for sensor networks. Then we offer a method for accurate and practical evaluation of routing protocols in sensor networks. We name it Special evaluation method and compare it with traditional evaluation method. Then, we show that our offer method has more accurate results than traditional evaluation method.??Finally, We find reasons of result difference between two methods.