Abstract: Thermoelectric cement-based composites have emerged as a research focus in functional materials. When used in complex environments such as oceans and salt lakes, the materials will be affected by a variety of ions, among which the most abundant chloride ions will have a significant effect on the thermoelectric properties of the materials. However, there is a lack of systematic research on the specific mechanism of the effect of chloride ion penetration on the thermoelectric properties of materials. Therefore, in this thesis, the thermoelectric properties of cement mortar composites with different carbon fiber contents (0.3wt%~1.5wt%) were investigated, and the effects of chloride ion penetration on their mechanical and thermoelectric properties were thoroughly studied. The experimental results showed that the composite with 0.9wt% carbon fiber content had the best mechanical properties (53.51 MPa) and high Seebeck coefficient (784.42 μV/℃). The porosity of the carbon fiber cement mortar composites was reduced and their compressive strength was enhanced by the effect of chloride ion penetration. Meanwhile, the chloride ions as charge carriers greatly increased the electrical conductivity from 3.74×10⁻⁷ S/cm to 4.67×10⁻⁴ S/cm. However, the interaction between the ionic thermoelectric effect induced by chloride ions and the cavity thermoelectric effect generated by the carbon fibers resulted in a gradual decrease of the Seebeck coefficient with the increase of the chloride ion content. Eventually the hybrid conductive effect formed by chloride ions and carbon fibers synergistically improved the power factor up to 1.82×10⁻² μW·m⁻¹·K⁻², revealing the dual role of chloride ions in optimizing the thermoelectric properties. This research provides theoretical support for the potential application of thermoelectric cement-based composites in marine environments or deicing salt environments.