Abstract:On the basis of discussion about the ontological status of quantum state in quantum mechanics, the properties of particle in the quantum theory of fields and the problem of time in the canonical quantum gravity, the author argues that the hard core of any physical theory consists of some metaphysical assumptions. The author points out that from the perspective of the history and philosophy of science, the relationship between philosophy and physics is in some way analogous of that between mathematics and physics, so the reunion of philosophy and physics will help us to clarify and even solve those fundamental problems in quantum theories.