Causes of scale deposition in flue gas turbine expander of FCCU were analyzed based on some aspects,including the types and operating conditions of flue gas turbines,properties and composition of feedstocks and catalysts,and operating conditions of the reactor and regenerator.Some countermeasures were proposed for preventing scale deposition in flue gas turbine of FCCU. Causes of scale deposition in flue gas turbine expander of FCCU were analyzed based on some aspects, including the types and operating conditions of flue gas turbines, properties and composition of feedstocks and catalysts, and operating conditions of the reactor and regenerator. for preventing scale deposition in flue gas turbine of FCCU.