The failure phenomenon happened in a certain model of High-Voltage Electric Connectors(HVEC) after voltage impulse testing is studied by applying testing methods of x-ray inspecting, internal checking, metallographic analysis，etc. The testing results reveal that several defects including multicore wire crimping damage and wire stripping injury are found in these devices. According to their failure mode and testing outcomes，the failure mechanism is analyzed and many reasonable improving approaches from the aspects of devices design，processing control and quality monitoring are suggested. After implementing these recommendations, the newly manufactured high-voltage electric connectors can pass all the examining items and their reliabilities are greatly enhanced.