The operational procedures for efficiently reconstructing the two-dimensional image of a body by the filtered back projection are described in this paper. The projections are interpolated for four times of original projection by zero-padding the original projection in frequency-domain and then inverse fast Fourier transform (FFT) is taken to improve accuracy. Nearest interpolation is applied to decrease operation time. Projection dependence of next pixel at the same row is used. For each row of image, the first pixel projection once for each angle is pre-computed, other pixel projection of this row can be found by iteration. Therefore, the pre-interpolation process only has to be performed once for each row, rather than individually for each pixel. It greatly reduces the amount of computation. Compared with original implementation, the speed of reconstruction image is nearly improved by five times. The image accuracy is still preserved.