Based on the charge balance principle, an optimal impurity distribution VLD termination (OID-VLD) and its ion-injection mask design method are proposed and verified. The comparative simulations and experiments show that OID-VLD can achieve better blocking ability and reliability than the traditional VLD (T-VLD). Vertical Double Diffusion MOSFET (VDMOS) with OID-VLD achieved breakdown voltage (BV) of 1684V and passed the 168 hours 100℃ -110℃ -120℃ -125℃ high-temperature reverse bias (HTRB) test, while VDMOS with T-VLD obtained BV of 1636V and failed in the 20 hours 120℃ HTRB test.