Abstract: Under the background of strategic ocean and double-carbon, it is important to use cathodic protection (CP) technology to enhance the service life of offshore structures. However, it requires additional power supply for extra drive. Here, nano-size nMnO₂ was synthesized by hydrothermal method, and then was mixed into cement mortar along with carbon nanotubes (CNTs) to prepare nano-modified cement-based thermoelectric composites (NTEC). 20 NTECs were connected in series to form a set of thermoelectric power generation module, and combined with electrochemical methods to comprehensively evaluate the feasibility of NTEC thermoelectric module based on differential temperature power generation directly serving as a current supply source for the reinforcement CP system of offshore structure. Results show that: The thermoelectric coefficient and thermoelectric power factor of NTEC specimens doped with 0.2wt%CNTs and 5.0wt%nMnO₂ can be up to 3612 μV/℃, and 301.4 μW·m⁻¹·℃⁻², respectively. The intrinsic mechanical strength and anti-permeability are accordingly guaranteed. Applying the CP based on the temperature difference power generation of NTEC, the corrosion potential of the reinforcement bar positively shifts, and the probability of corrosion is significantly reduced. Applying the CP based on the NTEC thermoelectric module the corrosion current density of the reinforcement is reduced by 3 orders of magnitude, the corrosion charge transfer is suppressed, the corrosion rate is greatly reduced, the self-power supply of CP for reinforcement in offshore structures is realized, and its mechanical properties and durability are guaranteed when simultaneously serving as concrete cover.