Abstract: To study the effect of paste-aggregate ratio on the printing performance of 3D-printed concrete retaining wall materials containing coarse aggregate, the rheological parameters of concrete slurry under different paste-aggregate ratios were tested by ICAR rheometer, and the influence law and mechanism were systematically analyzed. In addition, a self-developed cantilever concrete 3D printing device was used to carry out a pilot test on concrete slurry under different paste-aggregate ratios. The results show that the 3D-printed concrete material containing coarse aggregate is significantly affected by the paste-aggregate ratio. Under the condition of low paste-aggregate ratio, the fluidity of the material is poor, and the time-dependent behavior is strong, which is not conducive to the pumping and extrusion of the material, and the plastic viscosity decreases sharply due to the premature loss of plasticity. The high paste-aggregate ratio will lead to the increase of free water in the concrete slurry, which is easy to cause the collapse and segregation of the material and affects the forming effect of the retaining wall structure. In order to ensure the printing performance of 3D-printed concrete retaining wall materials, it is recommended to control the paste-aggregate ratio in the range of 1.1–1.2. The research results will provide theoretical support for the application of 3D printing technology in the construction of underground filling retaining wall.