Einstein's theory of relativity revolutionized the view of space-time in physics, and its basic inferences have been continuously verified in the past 100 years. However, the theory of relativity is built on the basis of continuous and smooth space-time, and it cannot be compatible with the concept of discrete space-time in quantum mechanics, which causes many difficulties in the development of modern physics. This paper presents for the first time a heuristic viewpoint in which space-time is considered to be a type of quantized waves propagating at the speed of light. Based on this concept, it re-explains many inferences of special relativity and general relativity, proposes new theory on gravitation and space-time, and provides a preliminary unified framework for explaining dark matter, dark energy, gamma-ray bursts, high energy emission mechanisms in quasar, the origin and evolution of the universe and other difficult problems in modern physics.