Disclosed is an organic amine salt foaming agent, that is, a composite polyurethane foaming agent, comprising: 1) hexafluorobutene; and 2) an alkanolamine salt mixture (MAA), the alkanolamine salt mixture (MAA) contains an organic amine salt compound having the following general formula (I): An−[Bm+]p (I); wherein An− is one or two or three selected from the following anions: (b) carbonate: CO32−; (c) formate: HCOO−; (d) bicarbonate: HO—COO−. A polyurethane foaming method using carbon dioxide and an organic amine in combination is also disclosed, in which carbon dioxide is added to a polyurethane composition for foaming. A method for preparing an alkanolamine carbonate salt with low water content from ammonium carbonate and an epoxide is additionally disclosed, in which a liquid alkanolamine salt mixture is used as a dispersion medium or as a solvent for reaction raw material.