Abstract: According to the design in which there are 18 detectors in Hard X-ray Modulation Telescope system of astronomical satellite, the authors propose two ways to fast implementation of the direct demodulation imaging method. One is calculation and storage method for Lucy iteration based on nonzero elements of point spread function of detector collimator, according to the fact that there are a large number of zero elements in point spread function. The other is to substitute Lucy iteration on the ordered subsets of observed data for Lucy iteration on all data in the direct demodulation imaging method. The numerical experiment results show that the imaging convergent speed of the direct demodulation imaging method is accelerated dramatically using the ways proposed in the present paper.