The invention discloses a collimator used for a detector and application of the collimator. The collimator includes a bottom plate, a shielding ring and a top plate. Imaging through holes are formed in the bottom plate in an array form, each imaging through hole includes a first hole section and a second hole section, the transverse size of the first hole segment decreases gradually in the direction from the free end to the second hole segment, the transverse size of the second hole segment decreases gradually in the direction from the free end to the first hole segment, the shielding ring isformed on the bottom plate, the top plate is arranged in the shielding ring, at least one part of an opening of the shielding ring is sealed, shielding through holes are formed in the top plate in anarray form, and the imaging through holes and the shielding through holes are arranged in the one-to-one correspondence form. According to the collimator, the top plate is used for secondary shieldingof radiation rays passing through the imaging through holes, overlapping between different pinhole projections is effectively reduced, and the production cost of the collimator is reduced.