A central air-conditioning system, comprises a plurality of air-conditioning assemblies (1) and a plurality of range hood assemblies (2); each air-conditioning assembly (1) comprises a compressor (11), a first heat exchanger (12) and a second heat exchanger (13) which are connected with each other through refrigerating medium pipes (14); all the range hood assemblies (2) are in communication with the public flue (6); a third heat exchanger (3) and the second heat exchanger (13) is connected through a secondary refrigerant channel (4); each end of each secondary refrigerant channel (4) respectively exchanges heat with the second heat exchanger (13) and the third heat exchanger (3). As all the range hood assemblies (2) are in communication with the public flue (6), the third heat exchanger (3) exchanges heat with the second heat exchangers (13) through the secondary refrigerant channel (4), when the system is operating, the heat energy generated by the air-conditioning assemblies (1) can be discharged through the public flue (6).