Abstract: Philosophical hermeneutics is criticized for leading legal hermeneutics to the trap of subjectivism and destroying the certainty of law from two dimensions of systems and epistemology. The first criticism means that the judicial system of China is so imperfect that legal hermeneutics should not learn from philosophical hermeneutics with subjectivism. The second criticism means a thing in itself which philosophical hermeneutics puts forward can not distinguish illegitimate prejudices from legitimate ones,so that philosophical hermeneutics failed to make the knowledge of laws succeed in avoiding the trap of subjectivism. That the relevant content of Truth and method as a classic of philosophical hermeneutics proves that presentation of a thing in itself is the criteria of distinguishing legitimate prejudices from illegitimate ones and verifying the knowledge of laws. As a result,the criticism of subjectivism is responded effectively. Therefore,legal hermeneutics should be the one that is based on the ontology of philosophical hermeneutics and belongs to legal epistemology in the future. It should not be a methodology of legal interpretation for which traditional epistemology lay the foundation.