The invention discloses a method for determining the upheaval quantity after reinforcing of a ballastless track low-embankment base expansive soil pile foundation. The method provides support for reinforcing design of the ballastless track low-embankment base expansive soil pile foundation, so that reinforcing design of the expansive soil pile foundation has better pertinence, and thus the upheaval resistance reinforcing effect of the expansive soil foundation is effectively improved. The method comprises the following steps that through actual sampling, actual measurement or research, the atmospheric influence depth or the water immersion influence depth l, with the unit being m, of the expansive soil foundation is determined; through on-site actual exploration, the neutral point depth l0, with the unit being m, of the reinforced pile foundation is determined, wherein the neutral point is the position where the upheaval quantity of foundation soil is equal to the pull-out quantity ofthe reinforced base foundation; and the upheaval quantity se after reinforcing of the ballastless track low-embankment base expansive soil pile foundation is determined through the formula in the specification.