A mixing model for the calculation of laminar flame speed of lean premixed H-2/CO fuel blends was derived through asymptotic analysis coupled with a reduced chemistry mechanism. The model was developed following the similar procedure given for the single component fuel. According to the different dominant effects of H-2 in H-2/CO/air flame, two separated algebra formulas were given when H-2 content was smaller or larger than 15%. Validations of the proposed model, as well as several existing mixing models were conducted against the experimental data of H-2/CO premixed flames reported in the literature. Results showed that existing models were either remarkably under-predicted or inconvenient to predict the laminar flame speed of lean premixed H-2/CO/air flames. The proposed model predicted well the experimental data over wide ranges of equivalence ratios (0.6-1.0), fuel compositions (1-100% H-2 in the fuel blend), and unburned gas temperatures (ambient to 600 K). In addition, its predictions also agreed well with the simulation results with detailed chemistry and molecular transport over a wide range of pressures (ambient to 20 atm). It is expected that the proposed mixing model can be cost-effectively used in relevant engineering CFD modeling with acceptable accuracy. (C) 2014 Elsevier Ltd. All rights reserved.