The invention discloses a silt-cement light building block, a method for preparing the same and application of the silt-cement light building block. The silt-cement light building block comprises, by weight, 13-56 parts of cement, 17-19 parts of coal ash, 15-69 parts of silt, 0.7-3.6 parts of foaming agents, 1.2 parts of foam stabilizers and activators. The weight of the activators accounts for 6% of that of the foaming agents. The method includes metering the cement, the coal ash, the foam stabilizers, the activators, water and the saturated silt and then feeding the cement, the coal ash, the foam stabilizers, the activators, the water and the saturated silt into a stirring machine; uniformly stirring the cement, the coal ash, the foam stabilizers, the activators, the water and the saturated silt to obtain first mixtures, then metering the foaming agents and adding the foaming agents into the stirring machine; stirring the foaming agents and the first mixtures briefly to obtain second mixtures, pouring the second mixtures in molds and maintaining the second mixtures. The silt-cement light building block, the method and the application have the advantages that energy consumption can be reduced during production, and the building block can be lightened, has certain strength and is low in production cost.