The invention relates to a half band filter method which is used in interpolating filter of digital to analog, it belongs to technology field of signal process. This half band filter method adopts mode of coefficient commix base decomposing, and combines concept of multi phase filter, by delaying consignation, adding from beginning to end, sampling and maintaining, weighting and adding, modulating and accelerating, taking out and zooming plus to half band filter. The advantages of the invention are following: the half band filter adopts method of coefficient commix base decomposing, and combines concept of multi phase filter, long shift operation can not be generated, data converting precision can be improved greatly, and complexity degree of program can not be added; using the half band filter of the invention, the design of flow and modularization are easy, and the hardware, territory distribution are more normal, it provides base of research and practice for automatization design and synthesis of filter system.