Abstract: The airplane/engine performance matching of a propfan requires that the engine performancesare evaluated over the entire range of Mach numbers and altitudes. The problem of the critical engine sizing requirements is considered firstly, an aerodynamic model is then provided to estimate the propfan efficiency trend and to determine the pressure drop in each expansion unit under the off-design conditions. Based on this model, two curves,ηB = f(SHP/D²)and -ηBR = f(J), are recommended to reduce the propfan efficiency map, and a redistributioncurve of the generalized pressure ratio over each expansion unit is obtained. According to these curves the off-design performances of a propfan,inclusive of the flight, take-off, and throttle characteristics, are predicted.