To investigate the feasibility of using novel reinforcing materials to replace fibers to improve the bending toughness of concrete, this study used 3D printing of polylactic acid (PLA) to prepare metamaterials and embedded them into cement-based materials. The crack evolution and mechanical properties of metamaterials and polypropylene (PP) fibers under bending load were studied by using three-point bending and acoustic emission measurement technology. The fracture behavior of metamaterials and PP fibers and the effects of metamaterials on the bending toughness of cement-based materials were analyzed from a microscopic perspective. The results show that the flexural strength of specimen embedded with metamaterials is 40.4% higher than that of specimen with PP fibers, and 116.8% higher than that of control group. Metamaterials greatly enhance the flexural strength of cement-based materials, changing the failure mode from a single crack mode to multiple crack modes, and brittle failure to plastic failure. PP fibers only increase the flexural strength of cement-based materials. The proportion of tensile cracks in the stable growth stage and instable cracking stage of metamaterials is significantly higher than that of PP fibers, and the toughness index is 16.75 times and 4.37 times that of PP fibers.