A CT collimator comprising a rotating slot part on a rotation shaft and having a plurality of blades, each blade has a slot of a different width and a radiation beam entering the collimator can only pass via a slot in one of the blades, each edge of each blade slot along a longitudinal direction has a convex curved surface structure, and in a vertical plane along a longitudinal direction, two side edges of the slot are curved, and each blade is arranged to be eccentric to the center of the rotation shaft. A CT system using the CT collimator, the detection area of the radiation rays projected to the radiation detector via the CT collimator can be maintained unchanged by adjusting the rotation angle of the blade, under the circumstance where the focus of the radiation source shifts during a CT scan.