As the key equipment in the flexible looped network controller and UPFC,the reliability of the modular multilevel voltage sourced converter directly affects the safe and stable operation of the whole AC system.We established a 3-D model of the flexible looped network controller and Sunan 500 kV UPFC converter using PTC CREO and ANSYS.We calculated the electric field distribution of the converter valve in insulation type test.The results show that the insulation strength of the air gap distance to the ground of converter valve,the air gap between layers of converter valve,the air medium outside of converter valve can meet the requirements of the converter valve in insulation type test,which can ensure safe and reliable operation of the converter valve.