The invention proposes an optimization method and system of a fuel gas system based on heat value balance, and relates to the field of fuel gas system control. The method comprises improving the production and consumption balance rate of a fuel gas by means of meter calibration and newly-added meters, and tracking the change of the heat value of the fuel gas; obtaining the optimal fuel heat valuerequirements of respective fuel consumption devices by using the thermal efficiency of a heating furnace as an evaluation index and by using a data mining method; performing pinch point analysis to obtain the best supply and use matching network of the fuel gas, and optimizing and reforming a fuel gas pipe network based on this, and constructing an operational optimization model of the fuel gas system by using the fuel heat value requirements, the fuel consumption and the pressure requirements of respective heating furnace as constraints, and giving a recovery scheme of effective components inthe gas, a fuel replenishment scheme and an fuel optimal distribution scheme; performing steady-state detection on the fuel gas system and executing an optimized operation plan on the basis of ensuring the stable operation of the system to achieve optimized and efficient operation of the fuel gas system and to improve the overall economic efficiency of a refinery.