Abstract: Based on discussions of the two fundamental ways of thinking in modern science, namely reductionism and systemism, we point out that complexity science, in which physics and its related interdisciplinary studies are deeply involved, is a vital territory in the development of contemporary science. Investigations on the particular characteristics of complex networks can be useful in the description of the structure and functions of various complex systems. As an introduction, we list the major schools in the field of complex science worldwide. Research on complexity and cross-disciplines is of deep significance in China's long-term scientific development.