OBJECTIVE： To provide the empirical basis for improving full coverage policy of essential medicines in China and promoting the fairness and accessibility of medicine. METHODS： Taking Taizhou diabetes essential medicines full coverage policy as an example， the electronic health records of diabetic patients in Taizhou city from 2011 to 2017 were collected， and the cost burden of patients was evaluated by whether catastrophic expenditure of family drugs had occurred. The concentration index was used to analyze the fairness of catastrophic expenditure on household medicines， and the effects of various influencing factors on the fairness of local medicine expenditure affordability were evaluated by year-by-year comparing the relevant indexes from baseline year to the third year of policy implementation. RESULTS & CONCLUSIONS： The concentration index of catastrophic expenditure on household medicines is negative from baseline year to the third year of policy implementation， which indicates that catastrophic expenditure on household medicines for diabetic patients in Taizhou mainly occurs in low-income groups. From the result of decomposition of concentration index， among the factors that affect the fairness of catastrophic expenditure on drugs in diabetic families， the contribution rate of  “taking free essential medicines” keeps at top five places year by year， and the contribution value is positive， which shows that the implementation of policies is conductive to reducing the unfairness of catastrophic expenditure on household medicines in low-income families. Full coverage policy of essential medicines effectively improves the fairness of medicine expenditure affordability. In addition， scientific and reasonable essential medicines selection mechanism， the guarantee level of the policy， collaboration with multiple factors should be promoted so as to improve the fairness and accessibility of essential medicines.