Significant disparities in breast cancer screening coverage existed between high-income and low-income regions. This study aims to assess the implementation, effectiveness, and sustainability of a breast cancer screening program in China to provide insights into developing an effective implementation strategy suitable for rural areas with limited health resources.This study employed the Reach, Effectiveness, Adoption, Implementation, and Maintenance (RE-AIM) framework to assess the implementation, effectiveness, and sustainability of a breast cancer screening program in Ordos, Inner Mongolia, China. An explanatory mixed methods design was applied, in which qualitative data were used to explain unexpected quantitative findings. The quantitative study, conducted from 2016 to 2020, analyzed screening records and survey data from 177,107 women aged 35-64. The qualitative study, conducted in 2024, collected data through semi-structured interviews with nine health workers and analyzed the transcripts using thematic analysis. The qualitative themes and quantitative findings were matched within the RE-AIM framework.The screening program covered 52.24% of the women by the end of 2020, with a total of 177,107 women receiving screening. The cancer detection rate was 0.56/1000, ranging from 0.09/1000 in women aged 35-39 to 1.58/1000 in those aged 60-64. The Positive Prediction Value (PPV) for biopsy was over 64.9%, but few patients who were referred for further examinations (mammography and biopsy) completed the procedure. Key facilitators included strong patient-provider communication, staff involvement, adequate funding and training, and strict supervision, while barriers involved geographical distance, lack of multi-sector support, limited service capacity, and low health awareness. The "rural outreach" model (where MCHHs conduct screenings by visiting rural villages and setting up temporary clinics at local village health centers), along with routine hospital screening, was seen as the most effective solution for reaching dispersed populations with low health awareness and literacy. Increased awareness from prior screenings improved participation and compliance in subsequent programs. A key challenge in program maintenance was the reduction in quality control, supervision, and training efforts.To improve cancer detection in rural areas, it is essential to strengthen both the screening capacity of primary healthcare facilities and the patient referral system for timely diagnosis. "Rural outreach" is an effective way to reduce health inequity in marginalized women and increase their awareness at the same time. Further research is needed to assess long-term outcomes and develop customized implementation strategies for overcoming the identified barriers.© 2025. The Author(s).