The invention relates to a foam light-weight concrete material used in a railway subgrade bed bottom layer. The invention, aiming to a defect existing in a railway subgrade fill-constructed by a granular rock and soil material, discloses an engineering material for replacing a conventional filling material in the railway subgrade bed bottom layer. In the technical scheme, the foam light-weight concrete material used in the railway subgrade bed bottom layer is formed from following components: cement, water, a foaming agent and an additive agent in proper ratios, and is produced by means of a concrete technology through hardening by a physical-chemical reaction. The foam light-weight concrete material can replace a conventional filling material in the railway subgrade bed bottom layer. The foam light-weight concrete material is light in weight, is strong in integrality, is high in strength, is stable in performance, is free of plastic deformation, is short in construction period and is reduced in depth of treatment of the railway subgrade layer. The foam light-weight concrete material can ensure trains to run stably and comfortably, can reduce subgrade defect, can save maintenance cost during operation, and is especially suitable for fill-construction of a high-speed railway subgrade.