In the past decades, natural gas has been, sharply, used as an alternative fuel in industrial sector, power generating system, furnace and various type of burner. Natural gas has higher heating value, low emission and low price in comparison to other fossil fuel. Combustion of various type of fuel (solid liquid and gas) has been studied for a long time. However, because of complex essence of combustion which is a combination of different physical and chemical phenomena, where are still a lot of work should be developed to improve combustion efficiency of thermal system such as burners. In current paper, laminar flame of natural gas produce by "Iraq, Saudi Arabia, Iran, Turkey, Indonesia and China" have been   studied in a freely propagation combustion tube. Numerical calculation of laminar flame speed, flame temperature and heat released were performed based on one dimensional model using CHEMKIN PRO. Results show that the highest flame speed occurs at an equivalence ratio range of 0.95 and 1.05.Simlar pattern is observed for flame temperature .This means that both laminar flame speed and flame temperature are peak of an equivalence ratio of 1.0.However, the effect of initial pressure on the combustion the natural gas- air mixture on flame speed, flame temperature and heat is observed to be opposite to that accursed of equivalence ratio. Moreover, the effect of initial temperature is quite positive. Since the flame speed, flame temperature and heat released increases. All obtained results show good agreement with other researchers.