The objective of this paper is to model the main reactions that take place in the Claus reactor furnace and compare it with actual data and simulated process. Since the most important point is the selection of suitable reaction conditions to increase the reactor performance, the model is formulated to predict the performance of the Claus plant. To substantiate the theoretical model, we used actual process condition and feed composition in Shahid Hasheminejad Gas Refinery. Model equations have been solved by using MATLAB program. Results from MATLAB are compared with those from SULSIM^? simulator and with actual plant data. The AAD (Average Absolute Deviation) of modeling results with actual data is 2.07% and AAD of simulation results with real data is 4.77%. Error values are very little and show accuracy and precision of modeling and simulation. The predicting curve for different parameters of the reactor furnace according to variable conditions and specifications are given.