The invention discloses a lubricant injection device. The device comprises a first insulating outer pipe, a second insulating outer pipe, an insulating inner pipe, an injector and a handle, wherein one end of the first insulating outer pipe is connected in series with one end of the second insulating outer pipe; the injector is detachably connected to the other end of the first insulating outer pipe; the handle is arranged at the other end of the second insulating outer pipe; the insulating inner pipe is arranged in the first insulating outer pipe and slides along the axial extension direction of a piston rod of the injector under the driving action of the handle to drive the piston rod. By applying the lubricant injection device to add a lubricant to an isolating switch, a worker can add the lubricant to a junction of an edge of an isolating knife switch and a link mechanism without rod mounting operation, the personal safety of the worker is guaranteed, and the working efficiency is improved.