This study analyzes the inter-provincial differences in the outpatient chronic and special disease guarantee policies across four major categories of diseases, including digestive system diseases, nervous system diseases, heart diseases, and rare diseases. Drawing on policy documents and medical insurance statistics from 27 provinces, this study combines literature analysis and quantitative research methods to assess the inter-provincial differences. The research results show substantial inter-provincial differences in the scope of disease coverage, which is associated with some extent with general outpatient pooling levels in each province. The level of treatment guarantee for the same disease varies considerably across different provinces. In addition, the outpatient chronic and special disease guarantee system for rare diseases remains inadequate, with insufficient coverage. Three recommendations are proposed to address the above problems. First, the medical insurance treatment coverage system that emphasizes inpatient care over outpatient care should be reformed to improve the general outpatient care coverage system, while promoting the transformation of the chronic and special disease coverage model from expanding disease coverage to sharing cost risks. Second, it is essential to rely on big data technology to reasonably identify diseases with high medical costs, standardize coverage standards, and strengthen inter-provincial policy coordination. Third, this study recommends establishing a multi-level and diversified coverage mechanism for rare diseases to effectively improve the equity of outpatient coverage for chronic and special diseases.