This paper proposes the concept of both-branch fuzzy decision on X, which contains neutral universe(X^*≠{x}), and the optimal decision analysis model. In addition, the paper proposes decision judgement theorem, decision discernment theorem, decision surplusage-discarding theorem and hole-digging principle on decision factors universe X. Both-branch fuzzy decision has such characteristics as decision two-direction dependence character, decision piling-synthesis character, decision branch-separating character, decision branch-degeneration character, and decision non-fault character. The research results have found application.