This paper supposes that N=8 Extended Supergravity (ESG) can form the composite supermultiplets, and discusses the possibility of containing SU(5) Supersymme-tric Grand Unification Theory (SUSY GUT) in both composite supermultiplets {3/2,8}N=8SU(8) and {2,28}N=8SU(8) Under some harsh assumptions, it is possible to obtain 3 generations of leptons and quarks and satisfactory particle spectrum of SU (5) SUSY GUT in the {3/2,8}N=8SU(8) scheme. Under some reasonable assumptions, it is possible to obtain 5 generations of leptons and quarks (or after some modification, 4 generations) in the {2,28}N=8SU(8) scheme.