In this paper, the precursors of MgxCa3−x(PO4)2 powders with different magnesium contents were first synthesized by a liquid-phase precipitation method with simple operation and easy control of the reaction process. And the MgxCa3−x(PO4)2 slurry was used to print porous scaffolds by 3D gel-printing (3DGP), and then the scaffolds were degreased and sintered to improve performance, which simplifies the process and saves costs. The effects of different magnesium ions (Mg2+) doping contents on the precursors were investigated. When Mg2+ doping content is 0, 5 mol%, 10 mol% and 30 mol%, the particle diameters of the precursors are, respectively, 44.51 μm, 41.91 μm, 38.38 μm and 31.93 μm. The effects of different Mg2+ doping amounts on the biological and mechanical properties of the scaffolds were studied. When the doping Mg2+ content is 0, 5 mol%, 10 mol% and 30 mol%, respectively, the porosity of the scaffolds is 72.11%, 70.26%, 69.83% and 65.15%, and the strength is 1.04 ± 0.01 MPa, 0.73 ± 0.17 MPa, 0.23 ± 0.01 MPa and 1.89 ± 0.21 MPa, respectively. The degradation behavior was observed when the scaffolds were immersed in phosphate buffer saline for 8 weeks, which indicate that MgxCa3−x(PO4)2 composite scaffolds are expected to be more widely used in the field of bone defect repairing.