The mass of the Universe is dominated by dark matter, a type of matter that only has gravitational interaction. However, we know little about the nature of dark matter. In particle physics, sterile neutrino is a commonly proposed candidate of dark matter, which belongs to warm dark matter phenomenologically. Compared with the current standard cold dark matter cosmology, warm dark matter predicts differently on small scales of the Universe. We develop cold and warm dark matter N-body cosmological simulations with high resolution, to study the numerical effect of warm dark matter simulation in detail. Combined with semi-analytic models of galaxy formation, we compare the predictions of warm and cold dark matter cosmology on various properties of the Universe and on various scales, in order to break the degeneracy between cold and warm dark matter models, and hope to find out the best observations to constrain the phenomenological property of dark matter.