Abstract: Design structure matrix is an effective tool for design process optimization of complex product. The fixation of coupling intensity among tasks is the key to co nstruct design structure matrix (DSM), which plays a good role in the layout of DSM. This paper uses fuzzy analytic hierarchy process (FAHP) to construct sensit ive and variable fuzzy consistent judgment matrix (FCJM), and changes them into coupling intensity in DSM by a special algorithm. At last, the fixation of coupl ing intensity in second-hierarchy decelerating machine is given as the example to apply FAHP to fixation of coupling intensity in DSM. Compared with other meth ods, it has strong applicability and is easy to operate.