The use of gas mixture in high voltage circuit breakers for insulation and arc quenching can effectively reduce liquefaction liquid of the working gas. Aiming at the use of SF

6

/CF

4

mixture

the state parameters of SF

6

and CF

4

have been calculated. The state parameters of SF

6

gas are obtained by using the Beattie-Bridgman empirical formula as the state equation which is commonly used in engineering design. At the sam

e time

a formula derived from curve fitting to a new SF

6

saturated vapor pressure curve is used. The state parameters of CF

4

gas are calculated using the SRK equation as its state equation while the Riedel formula is used as the saturated vapor pressure equation. By calculating the state parameters of CF

4

and SF

6

the saturated vapor pressure curve and the equal density curve of SF

6

as well as CF

4

are drawn

which can be applied in engineering design. Meanwhile

the two curves can be utilized to analyze the liquefaction characteristics of SF

6

/CF

4

mixture. On this basis

the application of CF

4

and SF

6

state parameters in high pressure mixed gas circuit breaker is illustrated.