In an absorption chiller comprising at least two chiller modules connected to each other and a method therefor in which an evaporator, an absorber, a condenser, a low-temperature generator, a high-temperature generator, a heat exchanger, an absorption solution pump and a refrigerant pump are functionally connected to one another, and gas, oil, vapor or exhaust gas discharged from a gas turbine, a diesel engine or another process is used as a heat source for the low-temperature generator or the high-temperature generator, the at least two chiller modules are connected to each other such that chilled water flows through the respective chiller modules in series while cooling water flows through the respective chiller modules in parallel, and that directions of flow of the chilled water and the cooling water are longitudinally reverse to each other in at least one chiller module which includes a final outlet for the chilled water, and, in the absorber of each chiller module, absorption solution is sprayed in at least two stages so that a concentration of the absorption solution becomes weaker toward the inlet side of the cooling water.