The invention relates to preparation of a hydrophobic chain modified polyethyleneimine foaming agent capable of releasing carbon dioxide and an application of the foaming agent in polyurethane foam materials. The grafting degree of a hydrophobic chain of the hydrophobic chain grafted polyethyleneimine foaming agent capable of releasing carbon dioxide is 1%-45%, the hydrophobic chain contains 1-2 polypropylene oxide repetitive units, and the terminal of the hydrophobic chain is C1-C6 alkoxy. By constructing a novel foaming agent core-shell structure in which an outer layer is an alkoxy polypropylene oxide chain and an inner layer is a CO2 adduct of polyethyleneimine, the polymerization degree of an alkoxy polypropylene oxide side chain of a CO2 adduct foaming agent of hydrophobic chain modified polyethyleneimine is decreased to 1 and 2, so that the dispersity of the prepared foaming agent in a polyurethane white material is not decreased, the smooth foaming process is guaranteed, and compared with corresponding foaming agents with the polymerization degrees more than 2 under the same grafting conditions, the CO2 content of the prepared foaming agent is substantially increased.