Abstract: Driven by the continuous refinement of the performance requirements of microwave absorbing materials, microcapacitor structures have demonstrated significant application value in electromagnetic shielding technology through optimized design. In this study, layered double hydroxide (LDH) was introduced as an additive into carbon black (CB)-doped glass fiber (GF) reinforced nylon 6 (PA6) system composites by hot press molding process, and the effects of the LDH content and chlorine-ion intercalation on the microwave absorbing properties of the composites were investigated. The research results show that LDH and CB constitute a microcapacitor structure effectively enhance the microwave absorbing performance of the composites, and the optimal performance of the composites is achieved when the content of LDH is 3wt% and content of CB is 5wt.%, with the minimum reflection loss value of −40.36 dB. The doping of LDH not only promotes the formation of CB conducting pathways and increases the resistive loss of the composites, but also LDH as the dielectric layer of the microcapacitor can enhance the polarization loss of the composites through dipole polarization. Using the special memory effect of LDH, chloride ions can be successfully inserted into the LDH layers, which enlarges the layer spacing of LDH and enhances the polarization loss of the composites under the joint action of carbonate ions and chloride ions. The intercalation of chloride ions into the LDH layers not only broadens the effective absorption bandwidth of the composite (covering Ku band) but also reduces the thickness to 1.7 mm of the material, which opens up a new way for the design and optimization of microwave absorbing materials.