The relative studies on evaporation of fluorides in quad- and pent-ingredient slag series during electroslag remelting process are concluded and summarized. The thermodynamic analysis on volatile reaction of fluorides has been carried out by activity calculation model of slag components to get order of evaporation of fluorides in different basicity slag. Results show that as basicity of slag is between 3. 74 and 0. 84
the order of evaporative capacity of fluorides is MgF
2
> AF
3
SiF
4
> AlOF. As the temperature is more than 1 200℃
the slag containing fluoride especially containing higher and high fluoride exist obvious weight loss phenomenon. For slag ANF-6 (/%: 30A1
2
0
3
7OCaF
2
) at 1 400 ℃
in 100 g slag sample the evaporation rate of fluorides is up to 0. 68 g/min
and the evaporation of A
1F
3
and SiF
4
should be the main reason for weight loss of slag.