Computed laminography (CL) has a particular function in plate-type structure tomography. For CL reconstruction, slant angle of the central X-ray is an important parameter and must be calibrated accurately. A practical feasible calibration method to determine the slant angle is proposed. According to this method, a spherical phantom is fixed on the rotary table and turns a full 360 rotation. Then, image processing and the least-square fitting are performed to figure out the locus of the projection. Consequently, the slant angle is achieved in accordance with the property of the fitted ellipse. The experimental results prove that this method is easy to implement and meet the inspection requirements. (C) 2014 Elsevier Ltd. All rights reserved.