In this investigation, a two-phase design strategy based on the composite of mortar phase and coarse aggregate phase is proposed for designing 3D printable concrete (3DPC) with coarse aggregate. Coussot model and Krieger-Dougherty model were utilized to establish a quantitative relationship between the rheological property of 3DPC and the volume fraction of coarse aggregate, aiming to design 3DPC with coarse aggregate based on the mix proportion of printable mortar and thus facilitate the mixture design. It is found that the plastic viscosity of 3DPC with coarse aggregate is excessively high when the volume fraction of coarse aggregate reaches to a certain value, which is the main reason restricting the printability of 3DPC with coarse aggregate. The printability of 3DPC with coarse aggregate cannot be solely evaluated by yield stress, the plastic viscosity should be taken into consideration together with yield stress for evaluation as well.