This paper elaborates on the process flow of the fuel gas system in a 220 kt/a ethylene plant of a petrochemical company. Variations in the composition and flow rate of VOCs tail gas from the atmospheric tank farm cause fluctuations in the pressure of fuel gas network, which in turn leads to the instability in the coil outlet temperature (COT) of cracking furnace and the discharge of surplus fuel gas to flare. Based on the existing process flow, the surplus fuel gas is sent to the olefin unit or integrated into the fuel gas system after being pressurized by a compressor. The delivery valve is a gate valve, which requires manual operation by operators on site. It is difficult to make timely on-site adjustments, resulting in the situation that the fuel gas is frequently flared to control the pressure of fuel gas system. Through operational optimization and technical modification, the problems of black smoke emission from cracking furnace and pressure fluctuations in fuel gas network have been solved.