The article applies Revised Dalton's method for calculation of thermodynamic properties (i.e. specific enthalpy, specific entropy and specific volume) of unsaturated humid air and gas mixture after combustion in humid air turbine cycle. The research temperature range is from 280 K to 1600 K and pressure range from 0.1 MPa to 5 MPa. "Improvement Factor" and "Cutting Off Temperature" for unsaturated humid air are explored in depth. Two "Improvement Factor" formulas are proposed. The discovery of the changing trends of "Improvement Factors" reveals the fundamental behaviors of dry air and water vapor in unsaturated humid air. Another discovery is "Cutting Off Temperature". It is a crucial temperature point, above which the interaction of dissimilar molecules may be omitted. Revised Dalton's method may also be applied to gas mixture after combustion. The thermodynamic properties of unsaturated humid air and gas mixture after combustion are calculated by the Revised Dalton's method. The average error of Revised Dalton's method is within 0.1% compared to experimental data. (C) 2013 Elsevier Ltd. All rights reserved.