A method based upon the weighted total cross section (WTCS) theory is proposed to calculate the photo-ionisation cross sections and the radiative recombination rate coefficients between the fundamental level of CO and the main electronic states of its corresponding ion. Total photo-ionisation cross sections and radiative recombination rate coefficients are determined from the calculation of elementary vibrational photo-ionisation cross sections. Transitions between CO + (X, A and B) and CO(X) are considered. Total photo-ionisation cross sections and recombination coefficients are computed in the temperature interval 500-15000 K.