A new type of air supply system, chair-back air supply system (CASS), in an air conditioned railway carriage in China is firstly presented in the paper by simulating the types of air distribution commonly used in the carriage and by comparing the results with prototype experiment. And evaluations on therma comfort and economy are also carried out. It is found that the CASS has its special advantages of better air distribution and better energy saving by comparing it with the other conventional air supply systems. Furthermore, it is much easier for the system to work in with the setting of air-conditioning units in the lower part of the carriage, which will meet the trend of high-speed of the carriages.