The 3-D numerical simulation method is coupled with erosion and particle rebound models based on the results of high temperature erosion tests to systematically study the gas-solid two-phase flow characteristics of a flue gas turbine for the first time. The aerodynamic loss characteristics of the flue gas-steam mixtures and particle erosion mechanism in the flue gas turbine cascade under design and non-design conditions are investigated. The results indicate that the mixing loss of cooling steam and gas, secondary flow loss, and separation loss significantly affect the entropy increment of the rotor cascade. The isentropic efficiency of the flue gas turbine under the design condition is 78.74%. The radial inflow of wheel cooling steam from the axial clearance has a radial impact and mixing effect on the mainstream flue gas, enhancing the generation and development of the secondary flow vortex in the rotor cascade. When the dimensionless cooling steam flow rate is reduced from 1 to 0.6, the isentropic efficiency of the flue gas turbine increases by approximately 0.9%. By contrast, when the dimensionless cooling steam flow rate increases from 1 to 2, the isentropic efficiency decreases by 0.42%. The erosion rate of the leading and trailing edges of the rotor is higher than those at other streamwise locations. The erosion of the rotor leading edge and the blade-tip trailing edge is caused by the high speed impact of particles above 10 μm, while the erosion of the rotor root is caused by the grinding of 1-5 μm particles carried by the secondary flow.