In th is paper, some new hypotheses about decision2mak ing under uncertainty have been p ro2 vided. W ith these hypotheses, and w ith respect to the degree of event’ s uncertainty asw ell as peop le’ s risk aversion, a credible p rior p robability functien of decision2maker has been defined. It exp lains themulti2p ri2 or p robabilities ofMM EU by fuzzy p robability, and expands the connotation of themulti2p rior p robability. Then a expected utility model based on fuzzy p rior p robability has been developed. Th ismodel can be used in the decision2mak ing under uncertainty. F inally, the model has been used to resolve A llais paradox and Ellsberg paradox, and the solutions turn up trump s.