Increasing dense sampling of the illumination and detection offers an effective way of improving the image reconstruction performances of diffuse optical tomography (DOT). We describe a fast tomographic image reconstruction scheme for a transmission measurement on a slab in the non-contact spatial light DOT providing large measurement data. The proposed method is carried out with the spatial-frequency encoding in both the measurement (source, detection) and the image spaces, and involves a strategy for selecting the useful spatial frequency based on the tissue transfer function. The method is expected to considerably reduce the calculation time for reconstruction whilst retain the quality of the reconstructed images. Additionally, the procedure of the spatial-frequency transform alleviates the ill-posedness of the inverse problem. Results from the simulated data show that it takes only 10 s to reconstruct one absorption image with the proposed method and the speed is more than 400 times faster than that with the conventional one for 81×81 source-detector pairs. Moreover, the proposed method shows a higher quantitativeness ratio and a superior anti-noise capability than the conventional one.