The invention relates to a solid concrete brick and a preparation method thereof, and belongs to the field of materials. The solid concrete brick includes a first brick body and a second brick body; the opposite sides of the first brick body are separately provided with a convex portion and a concave portion, the convex portion of the solid concrete brick and the concave portion of another solid concrete brick are matched with each other, and the cross-section of the concave portion is trapezoidal; and the top end of the convex portion communicates with the bottom wall of the concave portion through a mounting hole, the second brick body is poured into the mounting hole, one end of the second brick body is flush with the bottom wall of the concave portion, and the other end of the second brick body is flush with the top wall of the convex portion. Raw materials of the first brick body include water, cement, micro-silica fume, fly ash, sand, crushed stones, a water reducing agent, flexible epoxy resin, and polymer fibers. The solid concrete brick is good in practicability, high in strength, long in service life, convenient to install, and the labor cost is saved; and the preparationmethod is easy and controllable to operate, and the strength of the solid concrete brick is effectively improved.