The invention discloses a recovery method of blast furnace slag water residual heat and method thereof. The recovery system of resudual heat includes a blast furnace slag system, a sedimentation tank, a hydrocyclone separator, a water pump, a heat exchanger, a steam turbine, a refrigerant condenser, a refrigerant pump. The recovery method is that applying bicirculating low temperature hot water generation system to recovery residual heat and penerating power. The specific process is: guiding the blast furnace slag water into the heat exchanger after preprocessing of impurity precipitation and transmitting heat to low boiling refrigerant; the low boiling refrigerant absorbing heat in the heat exchanger and entering the steam turbine for expansion of doing work; the refrigerant after doing wirk changing into low-pressure superheated steam, the low-pressure superheated steam entering the concenser to releast heat and changing into liquid refrigerant of low-temperature and low-pressure, then being sent to the heat exchanger by the refrigerant pump for absorbing heat, becoming the superheated steam again to push the steam turbine to do work. The invention can recovery residual heat of the blast furnace slag water and generate power, and reduce energy consumption in steel production; and reduce temperature of blast furnace slag water which is benefit to improve quality of blast furnace water slag and reduce discharge of sulphide in slag washing process.