Abstract: The local reconstruction with truncated projection data is a difficult problem in CT reconstruction field.Conventional reconstruction algorithms will product severe truncated artifacts.The rising BPF algorithm and POCS iterative algorithm can solve the local reconstruction problem,but their reconstruction efficiency and paralleling performance are poor.In this paper,aiming at special structural flat object,it is found that if the thickness and the horizontal length of local area satisfy some conditions,accurate reconstruction can be carried out using efficient FDK algorithm.The results of numerical experiments show that when the horizontal length of local region is bigger than 1/8 horizontal length of object and the thickness is less than 1/13 horizontal length of object,the reconstruction results are comparable with the true values.The reconstruction results of real data also confirmed FDK algorithm could reconstruct the local area of flat object well under the condition.