Abstract: Objective： Drug patent compulsory licensing system is very significant when a variety of unexpected diseases related to public health outbreak or the affordability of expensive drugs for serious diseases is low in some country. However， there are still no specific standards and methods to measure the affordability of serious diseases. Pharmacoeconomics， serving as a tool to measure drug economic efficiency， plays an important role in measurement of the affordability of drugs. Therefore， we discussed the introduction of pharmacoeconomics to drug patent compulsory licensing system at the theoretical level. Methods： We analyzed successful cases of drug patent compulsory licensing system used in other countries， found methods to identify the affordability of drugs， and analyzed the feasibility of pharmacoeconomics serving to measure the affordability of drugs in drug patent compulsory licensing system. Results and conclusion： We devided incremental cost effectiveness ratio to per capita GDP to determine a reasonable range of the price of drugs and found a scientific and quantitative method to evaluate the affordability of drugs. It can not only be applied in drug patent compulsory licensing system but also used to urge enterprises to cut price. However， we may face some difficulties when apply it because the development of pharmacoeconomics is still at an early stage in China.