Defect engineering can give birth to novel properties for adsorption and photocatalysis in the control of antibiotics and heavy metal combined pollution with photocatalytic composites. However, the role of defects and the process mechanism are complicated and indefinable. Herein, TiO2/CN/3DG was fabricated and defects were introduced into the tripartite structure with separate O2 plasma treatment for the single component. We find that defect engineering can improve the photocatalytic activity, attributing to the increase of the contribution from h+ and OH. In contrast to TiO2/CN/3DG with a photocatalytic tetracycline removal rate of 75.2%, the removal rate of TC with D‐TiO2/CN/3DG has increased to 88.5%. Moreover, the reactive sites of tetracycline can be increased by adsorbing on the defective composites. The defect construction on TiO2 shows the advantages in tetracycline degradation and Cu2+ adsorption, but also suffers significant inhibition for the tetracycline degradation in a tetracycline/Cu2+ combined system. In contrast, the defect construction on graphene can achieve the cooperative removal of tetracycline and Cu2+. These findings can provide new insights into water treatment strategies with defect engineering.