In this paper,the authors study the issue of foldover of regular(s~r)×s~n fractional factorial designs,where r(≥2) is an integer and s is a prime or prime power.A general decomposition structure of the foldover plan for a regular(s~r)×s~n fractional factorial design is obtained.The relationship between an initial design and its combined design are studied. This is done both for with and without consideration of the blocking factor.So the authors generalize the results about foldover from s~n regular fractional factorial desi...