The invention discloses a method for preparing a concrete expanded clinker by utilizing low-grade limestone. Low-grade limestone tailing is used as a main calcium raw material; acetylene sludge is used as an adjusting material for the calcium raw material; desulfurization gypsum is used as a sulfur raw material; high alumina gangue is used as an aluminum raw material; and the concrete expanded clinker is prepared from the following raw materials in parts by weight: 50-55 parts of low-grade limestone, 25-30 parts of acetylene sludge, 5-15 parts of desulfurization gypsum and 10-15 parts of high alumina gangue. The invention develops a new method for preparing the concrete expanded clinker in the manner of treating waste with waste, can efficiently solve the social problem of the pollution to ecological environment by industrial waste, can realize the resource reutilization, can reduce the production cost of the concrete expanded clinker, can promote the market competitiveness of the concrete expanded clinker and has obvious social and economic benefits.