Abstract: Complexity science and philosophical thinking were introduced into the research of sports training periodization (cycle) for the purpose of clarifying its essence and characteristics and try to find out a new development path. The research results show that the traditional theoretical research on sports training periodization is a systematic paradigm, with the systematicity as its basic attribute. Sports training cycle is not only a systematic sports training, but also a system of sports training. Its model shows the limitations of simplicity system including the composition, linearity and certainty, etc. However, the complexity of sports training is both an important feature of contemporary sports training science and a key issue in the study of sports training periodization. In order to adapt to the development needs of sports training science and improve the training quality and quantity, it is necessary to integrate the thoughts and methods of generating, non-linear, randomness into the sports training periodization, that is, the theory research should move towards the complexity paradigm.