Abstract: Deontic logic is a new realm of logic,deontic paradox is a new problem of deontic logic.The thesis introduces and analyses four kinds of famous and important deontic paradox .On thie basis, I mainly make a reaserch on Chisholm's paradox. I think that the key problem of Chisholm's paradox is how to express the conditional normative sentence.So I suggest that we ought to propose a kind of 2-dual deontic system so that we can deal with deontic paradox.