The only way to find the essence of freedom is to discuss the relationship between freedom and necessity, in which China has always considered Engels view authoritative. Engel argues that the freedom is the knowledge of necessity, which is used to transform the objective world. But this explanation is still a little bit simplified. The crux of the problem lies in how to understand the objective necessity and see it as a law set up by freedom itself. So we have to draw lessons from Kant, Hegel, Husserl and Heideggers views, and to make a more in-depth discussion from three aspects, i.e. the ontological relation between freedom and nature, the epistemological relation between freedom and rationality, and the methodological relation between freedom and logic, so as to overcome the traditional prejudice between subject and object, and truly achieve the intrinsic unification between freedom and necessity.