The invention relates to the field of comprehensive utilization of high temperature liquid metallurgical slag, in particular to a device and a method for preparation of mineral wool from blast furnace slag. The online device for preparation of mineral wool directly from hot slag includes: a blast furnace, slag ditch, a smelting furnace group and a centrifugal fiber forming machine. One end of the slag ditch is connected to a taphole of the blast furnace, the other end of the slag ditch is communicated with the metallurgical slag inlet of a first smelting furnace in the smelting furnace group, and the metallurgical slag outlet of a last smelting furnace in the smelting furnace group is communicated with the centrifugal fiber forming machine. According to the online method for preparation of mineral wool directly from hot slag, the slag is sent into the smelting furnace group, and silica sand is added to undergo tempering and heating till the slag achieves the target composition and target temperature, then the slag is sent into the centrifugal fiber forming mechanism so as to be made into mineral wool. The direct mineral wool making process provided by the invention makes full use of the sensible heat of the high-temperature liquid slag, improves the efficiency of mineral wool production process, saves the energy consumption of mineral wool production process, and has obvious energy saving and environmental protection advantages.