For the unclosed scanning data of fan-beam computerized tomography (CT) , a correction method of geometrical artifacts based on nonlinear optimization model is proposed. The marked and measured objects are scanned by this method, and the geometric parameters of the CT system are precisely estimated by solving nonlinear optimization model which is based on the scanning data. The geometric artifacts caused by geometric parameters and the unclosed scanning data are corrected. Simulation and experimental results verify that the correction method effectively decrease the gometric artifacts of CT images for the unclosed CT data.