Moire topography, a generation and analysis technique of moire fringes, is one of the techniques usually applied to three-dimensiond (3D) object shape measurement. Three kinds of methods, shadow moire, projection moire and digital moire, are mainly used to generate moire fringes. At present, low- pass filtering is used for extracting the moire fringes, since the low-frequency region contains lots of unwanted frequency components, the extracted moire fringes are not satisfactory and need to be improved. After theoretical analysis, a new method for extracting moire fringes, the band-pass filtering method, is proposed. This method can be used to extract moire fringes generated by multiplication, addition or subtraction of the reference fringes and deformed fringes by digital image processing. Compared with the traditional low-pass filtering method, the contrast of moire fringes with bandpass filtering is higher, and the intensity distribution is standard cosine. Besides, there is a phase shift of π between the moire fringes produced by addition and subtraction operation, so their bright and dark fringes are justly reversed. The correctness and validity of the proposed method and analysis have been verified by computer simulations and experiments.