The invention relates to a carbon dioxide separation technique, which is particular applied to an ion additive for carbon dioxide absorbent of organic amines, wherein, the ionic additive contains 0.01%-5% of Rb[UO2SeO4(OH).H2O] and 0.01%-5% Cu2(CO3)OH2. Compared with organic amines without the ion additive, the oxidation speed of the organic amines with the ionic additive can be reduced by around 50% and the electrochemical corrosion can be decreased by 40%.