An insulated package casing relates to the field of circuit maintenance. The structure is as follows: the two ends of a package casing (2) are of the same outer diameter, the inner diameter of the package casing (2) is cone-shaped, and an inner diameter A (1) is larger than an inner diameter B (3). The package casing (2) is made of insulating materials including polyethylene, polypropylene, rubber and the like. The package casing (2) is used for being connected with a package insulating layer of a secondary terminal line. The insulated package casing of the invention has the following beneficial effects: first, the working time for previous insulated package of a secondary terminal line is reduced by 2/3; second, the problem that a terminal line may be wrapped unreliably is solved; third, an absolute insulation safety effect is achieved; fourth, the package requirements of wiring terminals of two specifications are met; and fifth, the package casing can be made in different colors to play a role in distinguishing voltage and current identification.