Abstract: The law positivism believes that the legal effect condition appeals to the social fact,has nothing to do with morality.It cannot reasonably explain why the law is effective,it cannot distinguish between "compliance obligation" and "robber orders".At the same time,the author advocates that the legal effect should be brought to the legal creation of the legislator,because the legislator may be evil or good,and cannot avoid the practice dilemma of "evil law and law";The natural law school argues that the law must satisfy moral conditions and meet moral standards.But the claim has not been able to shake hart about "does not exist between law and morality conceptual connection",successfully against the natural law school of moral role and influence of the legal effect;Dworkin trying to open up the third way,focusing on how moral influence and role of adjudication practice and reasoning,which eventually as the referee according to law,through the constructive interpretation "in" and the moral of the double inspection of "moral",in short,the law of political moral principles from a set of melt injection,are derived and the present legal practice provides the best ethical moral. However,it is important to be aware of the role and influence of morality on legal effectivenes:legal and moral not necessarily correlation does not equal can be independent of the moral law,there is a correlation does not mean the moral law and morality is equal to the law.