The main activities of Philosophy of science, as a branch of philosophy, has been began since the last decade of 19th century, in the wake of some experimental scientists' attempts to establish new non-metaphysical foundations for inductive empirical sciences. The very notable point is that the nature of philosophy of science has not formed and developed in one, but in five stages. In this paper I will illustrate the five-stage formation and development of philosophy of science in 20th century in order to draw some the results from it. These five stages are: 1. Sprouting stage (1890-1918): the characteristic of this stage is the reconstruction of Newtonian physics by means of Mach’s instrumentalism, Poincare’s conventionalism and Duhem’s modified falsificationism. 2. Evolvement stage (1918-1935): in this stage, three pillars of logical positivism (reductionism, analytic-synthetic distinction, and verificationism) set the stage for logical reconstruction of science. 3. The classical stage (1935-1970): in which the logical reconstruction of science is accomplished by Popper’s and some logical positivist’s revisions of the pillars. 4. The Historicism stage (1960-1985): in this stage, some philosophers, especially Feyerabend and Kuhn based on the history of science, criticize and challenge the main principles of the previous stages. 5. The modelistic stage (1970-2000): in which through increasing the pragmatic and semantic tendencies in science, ‘theory’ is replaced by ‘model’.