The present disclosure provides a battery module, a secondary battery and a cap assembly thereof. The cap assembly includes a cap plate which is provided with a terminal hole and an electrode terminal provided to the cap plate and covering the terminal hole; the electrode terminal includes an outer surface; the electrode terminal includes a positioning hole which is recessed with respect to the outer surface and includes a first portion and a second portion, the second portion is positioned to a side of the first portion away from the outer surface; a section of the first portion parallel to a central axis of the positioning hole is trapezoidal; a size of the first portion gradually decreases in a direction of the first portion close to the second portion, and a minimum size of the first portion is greater than or equal to a size of the second portion.