Abstract: Objective: To discuss the evaluation effectiveness of dual-energy CT Mono technology in neoadjuvant chemotherapy (NAC) of breast cancer. Methods: Dual-energy spectrum CT images of 30 patients with primary breast cancer before and after neoadjuvant chemotherapy were collected, and the clinical efficacy was divided into two groups according to RECIST 1.1 standard, (1) NAC effective group, including complete response (CR) and partial response (PR). (2) NAC invalid group: included stable disease (SD), progressive disease (PD) cases. After operation, according to Miller and Payne (MP) pathological grading system, the patients were divided into (1) effective group, including the cases of MP grade 4 and 5, (2) ineffective group, including the cases of MP grade 1-3. Statistical analysis and comparison of NIC and rate of NIC change between effective and ineffective groups. Results: In the above groups, there was no statistically significant difference in NIC value between the groups before NAC, and the NIC value in the above groups after NAC had different degrees of decline, the difference among the groups was statistically significant. The NIC value difference between the groups at venous stage was more significant than that at arterial stage. Tumor volume change rate and ΔNIC were positively correlated. Conclusion: The decrease rate of NIC value is positively correlated with the efficacy of chemotherapy, and NIC value can be used as the evaluation index of NAC efficacy of breast cancer.