A ray emission device and an imaging system with the ray emission device are disclosed. The ray emission device comprises: a cylinder; a ray source disposed in the cylinder for emitting a ray; and a collimator disposed in the cylinder. The collimator enables the ray emitted by the ray source to form sectorial ray beams at a plurality of positions in an axial direction of the cylinder. The cylinder has a pencil beam forming part arranged over an axial length of the cylinder corresponding to the plurality of positions. The sectorial ray beams form pencil beams through the pencil beam forming part when the cylinder rotates around a rotation axis.