This paper expounds the important meaning to guarantee and raise the reliability taking precautions against fire calamities for the system of city lifeline engineering.It quotes a large number of fire and fail cases to explain that it is a complex system engineering to evaluate the abiity of the fire systems in the city lifeline cngineering.It epresents some methods to evaluate the reliability of complex systems, these methods are being used in the different trades at the present. After comparing these evaluation methods, this paper presents the advantages and defects of analy tical method of the fail tree.It also shows clearly that this method can completely be competent at the job to analyze the reliability taking precautions against fire calamities for the city lifeline engi neering.