The invention relates to a method for adjusting the extreme value of the electric field strength in an insulation layer of a high voltage power cable. The method is technically characterized in that an inner metal sleeve is arranged in the insulation layer of the cylindrical high voltage power cable, and the center of the normal projection circle of the inner metal sleeve coincides with the centerof a cable conductor part; the extreme value of the electric field strength between the conductor and the inner metal sleeve is calculated; the extreme value of the electric field strength between the inner metal sleeve and a ground metal shield layer, the ratio of the extreme value of the electric field strength and the length of the inner metal sleeve are calculated; and according to the relationship between the length of the inner metal sleeve and the ratio of the extreme value of the electric field strength, the length of the inner metal sleeve is adjusted to adjust the ratio of the extreme value of the electric field strength in the insulation layer of the high voltage power cable. According to the invention, the design is reasonable; the utilization ratio of an insulation material can be effectively improved; the voltage withstand level of the power cable can be significantly improved under the premise of the same amount of the insulation material; and the method can be widely applied to cylindrical high voltage power cables of the voltage level of 3kV and above.