The invention discloses 
foam concrete and a preparation method thereof. The 
foam concrete comprises a gelling material, light aggregate, water, admixture and 
foaming agent. The preparation method comprises the following steps: (1) pre-treating raw materials to prevent hard lumps and hard grains in the raw materials from depositing in foam 
slurry; (2) weighing each component according to a proportion; (3) preparing and adding foaming solution; (4) loading and stirring, namely, adding water into a stirrer, starting the stirrer, and adding 
cement, 
coal ash, 
perlite, waterproof agent, anti-freezing agent, water 
reducing agent and 
fiber into the stirrer in turn; (5) foaming, namely, foaming at the same time of stirring the 
slurry, sealing a valve firstly and then pressurizing the valve by an 
air compressor; (6) adding foam, namely, after the gelling 
slurry is well prepared, adding the foam into the gelling slurry under the state of stirring without stopping the stirrer; and (7) 
casting and molding, namely, when the slurry surface has no floating foam, finishing the preparation of the foam slurry. The 
foam concrete has the functions of light weight, water proofing, 
fire resistance, heat insulation, freezing resistance, 
cracking resistance, 
shock resistance and the like, and is particularly suitable for 
engineering insulating 
layers in cold areas and water-blocking and shock-resistant 
layers of underground 
engineering.