The CO emission characteristics of interacting hydrogen and methane partially premixed flames were numerically investigated. A counterflow geometry was introduced to establish interacting two partially premixed flames. An one-dimensional OPPDIF code was used to simulate the interacting flames. The GRI-v3.0 was used to calculate the chemical reactions. Emission index for CO(EICO) was evaluated to quantify the CO emitted from the interacting flames. The global strain rate and equivalence ratios for each flame(${Phi}_{CH_4}$ and ${Phi}_{H_2}$) were used as parameters to control the extent of interaction between two partially premixed flames. When ${Phi}_{CH_4}$ was kept to stoichiometric condition and ${Phi}_{H_2}$ was at rich condition, unburned H2 species of hydrogen flame was transported to the methane flame and affected reactions related with CO formation. When ${Phi}_{CH_4}$ increased from a stoichiometry to rich condition while ${Phi}_{H_2}$ was kept to stoichiometric condition, EICO increased initially, had a peak value at ${Phi}_{CH_4}=1.5$ and decreased gradually. This could be elucidated with an analysis for the elementary reactions related with CO formation.