The electric field of phase - phase , phase - earth of three - phase arc quenching chamber of the circuit breaker is calculated , insulation character is analyzed and the circuit breaker ' s whole insulating structure are ensured 计算了断路器三相灭弧室断口相间、相对地等的电场分布,对绝缘性能进行了分析,确定了真空断路器整体绝缘结构。