Budget impact analysis of drugs for rare diseases in different countries are reviewed. There are more than 7 000 kinds rare disease characterized by low incidence, serious influence on patients and society, difficulty in diagnosis, less effective intervention and therapeutic drugs. With the orphan drug legislation of the United States, the European Union and other countries, the number of drugs for rare diseases is increasing. At present, the United States has approved more than 600 drugs for rare diseases, and the European Union has approved more than 100 drugs for rare diseases. The types of rare diseases, the number of patients receiving treatment, the number of approved drugs for rare diseases, the annual cost of drug treatment for rare diseases and the availability of drugs are the main factors affecting the budget. The study shows that with the increase in the number of drugs approved for rare diseases, the proportion of drugs expenditure for rare diseases in the total drug expenses showed a slow rising trend, and there are national and regional differences. The overall budget impact of orphan drugs is small and fairly stable relative to total pharmaceutical expenditure. In addition, a small number of rare diseases drugs used to treat tumors and metabolic diseases have a greater impact on the total drug cost.