Though polymer crystallization has been intensively studied for decades, there are still some important questions remain open, such as microscopic mechanism of nucleation, existence of mesophase or not and variation of properties of crystal embryos with size, etc. In this proposal, we attempt to solve these challenges via the following strategy: First, a new model for polymer crystallization will be established, based on microscopic kinetics of attaching and detaching. The key of the model is the multibody-interaction parameters that correlate the macroscopic properties, such as energy barrier, surface free energy and lamellar thickness, to the microscopic parameters on molecular level. Matlab and Monte Carlo methods will be applied to simulate the evolution of polymer lamellae so as to reveal the microscopic mechanism of nucleation, lamellar thickening and melting. Second, the corresponding experiments will be designed to study the variation of lamellar thickness with temperature, the properties of the mesophase, and the difference between small molecule and polymer crystallization. The research is expected to develop a new theory on polymer crystallization and deepen our understanding of crystallization.