Lightweight foam soil for changing and filling special metro subgrade

The invention provides lightweight foam soil for changing and filling a special metro subgrade, relating to a building material. The lightweight foam soil for changing and filling the special metro subgrade is prepared from the following materials: cement, silica fume powder, diatomite, fly ash, water, a water reducing agent, an early strength agent, aluminium powder, sodium gluconate, plant fiber, a foaming agent and a micro foam agent. The lightweight foam soil is light, high in strength and good in overall performance, meets the need of the bearing capacity of a soil body of a soft soil area, also meets the need of the bearing capacity of the changed and filled subgrade per se on the load of the upper part, reduces the load of the special subgrade, and reduces subgrade settlement.