Due to large fluctuation on average COT temperature in two ethylene cracking furnace named EF⁃111M and EF⁃111N of No.1 petrochemical plant of PetroChina Daqing petrochemical company, an advanced control system of average COT temperature for the furnaces is designed and developed. Firstly, based on the existing problem of conventional control strategy, the advanced control strategy of average COT is designed. In addition, the non⁃minimal state space model predictive control (NMSSMPC) is used as the design of the average COT temperature controller. Finally, the developed advanced control system of average COT temperature is applied to M# and N# furnace of Daqing petrochemical company. Compared with the conventional control strategy, standard deviation between measurement and set⁃point of COT temperature in M# furnace decreases from 1.24 ℃ to 0.57 ℃ with the advanced control strategy. And the standard deviation of average COT temperature in N# furnace decreases from 1.84 ℃ to 0.72 ℃. The standard deviation of average COT reduces by 54.03% and 60.87% for M# and N# furnace, respectively. It can achieve the expected goal to remain average COT within 1 ℃.