The invention discloses a method for preparing a thermal insulating wall material by using waste bricks. The method comprises the following steps: firstly crushing the waste bricks and then smashing the crushed waste bricks with a ball grinding mill to obtain waste brick powder, then mixing bentonite, kieselguhr, sodium carbonate and stearic acid, adding triethanolamine, and grinding to obtain a modified enhancer; then adding the waste brick powder, cement, the modified enhancer, coal ash and water into a stirring kettle for uniform mixing to obtain a base material; finally adding a foaming agent, a water reducer and a compound exciting agent into the base material, uniformly mixing, and transferring into a mold for standing and forming to obtain the thermal insulating wall material. The thermal insulating wall material is prepared by using the waste brick powder as a main raw material and adding an appropriate amount of the modified enhancer, exciting agent and foaming agent, the obtained wall material is of preferable heat conductivity coefficient and compressive strength, and the material can be used as a wall body thermal insulating material of non-bearing structures.