The invention provides a mold for forming counter bores in side faces of a glass bottle mouth. The mold comprises a mouth mold and a pair of counter bore molding parts, wherein the mouth mold is matched with an initial mold of a glass bottle; the mouth mold is composed of two half mouth molds; a central cavity formed during the mold clamping serves as a mouth mold cavity; the interface of the twohalf mouth molds serves as a joint surface; a pair of symmetrically-arranged mounting holes are formed after the clamping of the two half mouth molds and used for mounting the counter bore molding parts; a pair of press blocks are correspondingly arranged on one of the half molds of the initial mold according to the positions of the counter bore molding parts; spherical balls in a pair of the counter bore molding parts can move towards the mold cavity along central axes of the counter bores by means of external force applied by the press blocks during the clamping of the initial mold to ensurethat a core head of a core column enters the mouth mold cavity; or the spherical balls move away from the mold cavity along the central axes of the counter bores by means of elastic force of reset springs during the opening of the initial mold to ensure that the core head of the core column quits the mouth mold cavity. Through the mold provided by the invention, the technical problem that the counter bores cannot be formed in a joint line of the glass bottle mouth in the prior art is solved.