[en] Possible structures of the gauge hierarchy of interactions are investigated for grand unification models, especially for the SU(L) model. Several sum rules are derived, which are relations between α, αsub(s), sin²theta sub(W) and possible threshold masses M sub(i) of new interactions. These sum rules reveal clearly and quantitatively correlations between the enlargement of the colour group and that of the flavour one. By applying these sum rules, possible steps of enlargement and the corresponding threshold masses M sub(i) are analyzed numerically. The modified SU(L) model with sin²theta sub(W) not equal 3/8 at the unification mass is also discussed, which involves new quarks with charge Q not equal n/3 and/or new leptons with fractional charge. (author)