Einstein published five famous physics papers covering three areas of the transition from classical physics to modern physics. The first and second papers clarified the nature of molecules and explained the "Brownian motion" of suspended particle statistics, which was of great significance for eliminating people's doubts about the reality of atomic physics at that time and opening up the general theory of statistical thermodynamics and stochastic processes. The third and fourth articles are devoted to expanding and perfecting Maxwell's theory, introducing special relativity, and expressing the famous equation E=mc2 for the first time. The fifth chapter proves that light is both a particle and a wave, explains the photoelectric effect of electrons emitted by a puzzling solid when it is irradiated by light, profoundly reveals the contradiction between the continuity of Maxwell field and the separation of particles, and becomes an important milestone in the development of quantum theory.