The invention discloses a method for carrying out CT imaging on the region of interest of an object to be detected, which comprises the following steps: acquiring CT projection data of the region of interest acquiring CT projection data of a B region selecting a group of PI line segments covering the region of interest, and computing the reconstructed image value on each PI line segment in the PI line segment group and then, combining the reconstructed image values on all PI line segments in the PI line segment group to acquire the image of the region of interest. The invention also discloses a CT imaging device adopting the method and a data processing unit in the CT imaging device. Because the two-dimensional/three-dimensional CT image of the region of interest can be accurately reconstructed and acquired only by covering the region of interest and the B region by the bundle of X-rays, a detector with a smaller size can be used for realizing the CT imaging of the region of interest in optional positions of an object with a large size, thereby greatly reducing the radiation dose of X-rays in the CT scanning process.
