Abstract: In this paper,the principle of local tomography algorithm by means of a new filter is expounded and the second error estimation is presented. The new filter with its side-peaks declining rapidly is adopted. Its decline rate is also proved to be the fastest among all the possibly selected filters, which will be detailedly discussed in other papers. The new filter features itself with favorable local tomography characteristics and remains its original features unchanged. The utilization of the new filter neglects the data far from the calculating point so as to realize the local tomography simply by CBP. The numerical experiment results of local reconstruction based on the simulation and experimental projection data show that the local tomography algorithm is much simpler and faster, even compared with regular CBP reconstruction using all the projection data. The resolution and Gibbs effects of the reconstructed images get improved.