We study the single ionization of CO molecule in orthogonally polarized two-color laser fields using time-dependent Hartree–Fock method. Employing the coherent superposition consisting of a fundamental field and its second harmonic, we consider different wavelengths (780 and 390nm) and intensities (1×1014, 1.5×1014 and 2×1014 W/cm2) of the fundamental field for which different ionization mechanisms are involved. Our numerical results reveal that the contributions of the three highest occupied molecular orbitals are strongly influenced by the intensity ratio and time delay between the two components of the bichromatic field. At the fundamental wavelength of 780nm and intensity of 2×1014 W/cm2, the two outermost molecular orbitals display a dominant response to the orthogonal two-color laser field when the second harmonic field is stronger than the fundamental field.