In the process of image super-resolution reconstruction, there is a need for interpolating pixels in the low- resolution image. On the basis of detecting the edge of low-resolution image and in consideration of its direction, the pixels belong to edges in the reconstructing high-resolution image are interpolated at first. Then, other zero -padding pixels are interpolated by using the bi-cubic method. By comparison with the results of nearest-neighborhood interpolation, bi-linear interpolation and the traditional bi-cubic interpolation, the result of this experiment on Lena image shows that the image edges are better persevered.