The thermogravimetry (TG) -differential scanning calorimetry ( DSC) analyses on 4 kinds of electroslag for remelting- AH-6 (70% CaF

2

)

M-l (42%CaF

2

)

L-3 (15% CaF2) and F-2 (free CaF

2

) have been carried out by using TG and DSC

the structure of melting slag at elevated temperature is measured by using X-ray diffraction (XRD) method. Results show that the gas-phase fluoride is forming by reaction between CaF

2

and other oxides in slag led to weight loss of slag and there is obvious difference between initial ingredient of slag and end ingredient of slag in slag pool； with increasing CaF

2

content in initial slag

the weight loss rate of fluoride increases

and at 1 500 ℃ the weight loss rate of slag AH-6

M- 1

L-3 and F-2 is respectively 11. 92%

7. 84%

4. 87% and 0. 38%. It is found to measure high temperature melting slag by XRD that the complex structure and higher melting point materials such as 2CaO • SiO

2

(2 130 ℃ )

3Al

2

O

3

•2SiO

2

(1 750 ℃ )

CaO

6Al

2

O

3

( 1 860 ℃ ) and 11CaO•7Al

2

O

3

CaF

2

( 1 577 °C ) occur in slag pool led to the ingredient segregation in formation of slag skin and the ingredient of slag pool and slag skin being no-constant in whole ESR process.