An air conditioning system includes a first circulation module and a second circulation module. Two circulation modules are joined by a heat exchanger. The first circulation is a modular refrigeration system includes a compressor, expansion device, and heat exchangers. The second circulation module includes a main liquid refrigerant tank, a number of distributed liquid refrigerant tanks, liquid pumps and a plurality of indoor units which includes a heat exchange device and a vapor propelling device. The heat exchange device is connected to the main liquid tank. The vapor propelling device propels the working fluid in a saturated vapor state to the first heat exchanger, thus forming a working fluid loop. It can be switched between the heating and cooling modes.