The invention discloses a foam inhibitor for a CO2-containing oil-gas well which is used for preventing CO2 from corroding oil-gas-well pipe columns in the processes of water discharge of a CO2 drilling stratum, CO2 injection for improving the oil-gas recovery ratio and CO2 heat exchange (hot dry rock or geothermal exploitation). The foam inhibitor comprises the following components: 100 ml of deionized water, 1-2 ml of an acid foaming agent, 0.05-0.1 g of an acid-resistant foam stabilizer, 0.025-0.05 g of a corrosion inhibition main agent and 0.02-0.05 g of a corrosion inhibition auxiliary agent, wherein the acid foaming agent is a mixture of fatty alkyldime thylamine oxides, ammonium sulfate lauric acid and glycerol; the acid-resistant foam stabilizer is a mixture of xanthan gum and dodecyl dimethyl benzyl ammonium chloride; the corrosion inhibition main agent is a mixture of quaternary ammonium bis-imidazoline, isopropanol, aminoethyl acid, diglycolamine, potassium iodide and ethyl alcohol; and the corrosion inhibition auxiliary agent is thiourea. The foam inhibitor is strong in applicability, good in water solubility and high in inhibition rate.