Abstract: Liquid sulfur is adopted in the coal direct liquefaction facility as a sulphide agent to convert the catalyst used in the coal liquefaction reaction from saturation to sulphide state to ensure its catalytic activity.At present, the sulfur injection is mainly injected by high pressure sulfur pump supplemented by low-pressure sulfur injection at the bottom of the catalyst slurry mixing tank.Due to the high failure rate of the high-pressure sulfur injection pump and the harsh process operation conditions, problems such as unstable sulfur injection, high energy consumption, and high maintenance costs have arisen, it is necessary to optimize the sulfur injection system.Pipeline is led out from the low-pressure sulfur injection point at the bottom of the existing catalyst slurry mixing tank and connected to the bottom of the oil-coal slurry mixing of the three series of A,B,C,replacing the original single-line low-pressure sulfur injection at the bottom of the catalyst slurry mixing tank with a four-series-pressure sulfur injection mode and stopping the high-pressure sulfur injection pump in due time.The optimization measure not only ensures the sulfonation and the stable operation of the facility but also saves about 570 000 yuan/year in equipment operation and maintenance costs.