The invention discloses a foam water-drainage agent and its aqueous solution, and belongs to the technical field of the oilfield chemical engineering. The foam water-drainage agent is composed of 50-80 parts by weight of a Sapindus mukurossi Gaertn extract, 20-40 parts of fatty alcohol polyoxyethylene ether AEO18, 1-5 parts by weight of polyacrylamide and 5-10 parts by weight of triethanolamine. The foam water-drainage agent has the characteristics of strong foaming capability after meeting water, good foam stability, and high liquid carrying capability and high mineralization resistance of foams, and is suitable for the use in natural gas wells containing gas condensate and having a high mineralization and a large water output; the foam water-drainage agent has a foam stability of 170mm, has a foam water content of not more than 2.0%, has a mineralization resistance of 250g/L, has a gas condensate resistance of 30%, has a temperature resistance of 90DEG C, is non-toxic, is easy to degrade, and does not pollute the environment; and the foam water-drainage agent has the advantages of compatibility with chemicals comprising methanol, a corrosion inhibitor, a scale inhibitor and the like, no chemical reaction with gas or liquid components, no increase to the toxicities of gases or combustion products, and no corrosion to equipment or pipelines.