Taking four major categories of diseases—digestive system diseases, nervous system diseases, heart diseases, and rare diseases—as the research objects, this paper analyzes the inter-provincial differences in the outpatient chronic and special disease guarantee policies for the above four categories by relying on policy documents and medical insurance statistics from 27 provinces, and adopting a combination of literature analysis and quantitative research methods. The research results show that there are extremely significant differences in the scope of disease coverage among various provinces, and such differences have a certain correlation with the level of general outpatient pooling in each province; the level of treatment guarantee for the same disease varies greatly among different provinces. Taking Alzheimer's disease as an example, the gap in its payment limit can reach several times. In addition, the outpatient chronic and special disease guarantee system for rare diseases is still imperfect, with insufficient guarantee intensity. To address the above problems, first, reform the medical insurance treatment guarantee system that emphasizes inpatient care over outpatient care, improve the level of general outpatient care, and simultaneously promote the transformation of the chronic and special disease guarantee model from "expanding disease coverage" to "cost risk sharing"; second, rely on big data technology to reasonably identify high-cost diseases, standardize guarantee standards, and strengthen inter-provincial policy coordination; third, establish a multi-level and diversified guarantee mechanism for rare diseases to effectively improve the fairness of outpatient chronic and special disease guarantee.