Chemical looping gasification technology is an effective way to realize the efficient and clean conversion of solid fuel. The autothermal operation of MWth scale chemical looping gasification is an important basis for the commercial application of this technology. Aspen Plus is used for simulation research in order to realize the autothermal operation of the chemical looping gasification demonstration unit. The reliability of the process model is verified by experimental data. The mass and heat balance of the 3 MWth coal chemical looping gasification system is solved. By analyzing the effects of reactor temperature, steam flow rate and temperature, cyclone separator efficiency, oxygen carrier active component content, and other process parameters on syngas yield, syngas component concentration, syngas H2/CO, solid circulation flow rate, and other process performance of the system, the autothermal operating conditions for maximum syngas production are determined. The results show that the net heat power of a 3 MWth coal chemical looping gasification system is close to 0, and the system tends to autothermal operation. The optimum operating conditions are fuel reactor (FR) temperature of 850℃, air reactor (AR) temperature of 950℃, steam flow rate of 305.25 kg/h, steam temperature of 300℃, and cyclone efficiency of 98%. At the same time, the solid circulation flow rate of the system is the smallest, which is about 10 555~10 580 kg/h. The total concentration of syngas (CO+H2) is the largest, which is about 75.1%. In addition, the use of ilmenite particles with higher content of active components as oxygen carriers is beneficial to reduce the solid circulation flow rate of the system.