The present disclosure provides an end cover assembly, an energy storage device, and an electric apparatus. The end cover assembly includes: a cover plate having a first through hole; a pole including a pole body, the pole body passing through the first through hole and provided with a first thread at an outer peripheral surface of the pole body; an insulator provided on the cover plate and having a second through hole, the second through hole having a hole wall provided with a second thread, the pole body passing through the second through hole, and the first thread being connected to the second thread; an anti-loosening structure including a first anti-loosening portion and a second anti-loosening portion that are engaged with and connected to each other to prevent the insulator from loosening.