A novel 3D-printing repair is proposed based on Fused Deposition Modeling (FDM) for improving the mechanical strength of the objects with surface cracks. Compared to the traditional FDM-based technique, the novelty of our proposed approach is that the extruding and moving directions of the printing nozzle are controllable and thus variable, eliminating any restriction of orthogonal alignment. This permits essential physical contact between the nozzle and the cracked area that allows the nozzle to remove surface material that might be covered by dust, as well as the heat transfer that preheats the inner material before being combined with the extruding one. Hence, the proposed approach can strengthen the bonding strength of materials to a great extent, particularly when the environmental temperature is not in a suitable range. Experimental results show that the mechanical strength of the objects with surface cracks is significantly improved by our proposed approach of 3D-printing repair compared to that produced by the traditional one.