Water granulating is widely used to treat blast furnace slag in iron-making process, and the large amount of waste heat of granulating water is currently wasted in the cooling tower or in detritus tank. In response to the status, a new-style technical scheme that the granulating water was used for building heating as the heat source was put forward in the paper. Based on the analysis calculation on the heat balance of the water granulating process, the technical scheme and the system optimization method were put forward in the paper, and a specific engineering in Jinan Iron&Steel group was calculated and designed. The result showed that the system could supply heating for the living district, and the water was cooled effectively for circulating utilization. It would gain great energy efficiency and environmental benefits.