Abstract: In view of the challenges of “undetectable and inaccurate monitoring” of cement sheath sealing integrity in oil and gas well cementing, a multi-threshold coupled self-sensing cement slurry development method was proposed, and a self-sensing cement slurry system tailored to the demands of cementing engineering was developed. The system utilizes Grade G oil well cement as the matrix and incorporates an electrostatically self-assembled carbon nanotube/nanocarbon black (CNT/NCB) composite functional material to achieve a synergistic long & short-range conductive effect, significantly enhancing the electrical conductivity and self-sensing capability of the cement slurry. Its electrical response characteristics were systematically tested under cyclic loading conditions (30%–70% of compressive strength). The test results indicate that the self-sensing cement slurry system has a transition time of 20 min, a flowability of 21 cm, a compressive strength of 54.5 MPa, and a strain sensitivity of 47. Its “mechanical-electrical” response capability is significantly superior to that of traditional cementing slurries, and the relative change rate of electrical resistivity is increased by six times. Furthermore, the changes in electrical resistivity are highly synchronized with stress and strain, enabling real-time diagnosis of microcracks within the cement sheath through electrical resistivity anomalies. The research results provide theoretical support and a material foundation for the precise monitoring of cement sheath sealing integrity in complex oil and gas wells.