The invention discloses a method for determining the actual maximum expansion rate of foamed asphalt. The method comprises the following steps of: 1) acquiring measured value ERm, half-life period tau 1/2 and injection time ts of the maximum expansion rate of the foamed asphalt under any foaming conditions; and 2) determining the actual maximum expansion rate ERa of the foamed asphalt according to the formula in the specification. The method has the advantages of convenience of calculation and accurate results. The ERa can be acquired according to the ERm, the tau 1/2 and the ts which are measured under any foaming conditions.