Faults happened on AC filter sub-bank circuit breakers (CB) would endanger the safe and stable operation of the power system. It’s necessary to analyze the factors influencing the insulation of arc-extinguishing chamber by simulation and calculation of the CBs to identify the causes of CB faults. Considering structure symmetry, a 3D calculation model including moving/static contact, porcelain coat, SF₆ gas and air package, is established by Solidworks software for one of the double breaks of 550 kV ceramic post breaker. Simulations of the 3D stactic electric field are carried out using ANSYS under five conditions: normal break, metal particles on porcelain, metal particles suspended between two arc contacts, metal particles on arc contact, and increasing inner diameter of porcelain. Results show that the maximum electric field happens 7.5 ms after arc is blown out, metal particles on arc contact will significantly increase the electric field intensity, CB insulation faults can be effectively reduced by raising the SF₆ gas pressure properly and using metal particle absorption measures.