The invention discloses a 3D (three-dimensional) printing method of a building structural wall, comprising the steps of mixing waste concrete powder and waste brick powder, crushing, grinding, drying,adding cement, and mixing well to obtain a first material; mixing carbon nanotubes, castor oil and water, heating, stirring, drying by spraying, adding formic acid and petroleum ester, mixing well, adjusting temperature for stirring, dropwise adding phosphoric acid solution, continuing to perform stirring, dropwise adding hydrogen peroxide, stirring, filtering, drying, adding a water reducer, iron tailings, nano zirconia, gypsum, iolite and nano spherical iron oxide magnet powder, and mixing well to obtain a second material; adding, continuing to perform stirring while adding the first material, the second material and bismaleimide, continuing to perform stirring until a viscous slurry is obtained, transferring the slurry to a 3D printing system, and performing printing to obtain the building structural wall.