Abstract: Nylon powder is a commonly used powder material in Additive Manufacturing whose fluidity is closely related to temperature. Exploring powder fluidity at preheating temperature in Additive Manufacturing is the basis for studying the fluidity and spreading properties of powder in selective laser sintering (SLS) process. Choosing nylon powder in SLS technology as a raw material and the flow behavior of nylon powder is studied by discrete element method (DEM), which is a hot topic of numerical simulation and powder spreading process optimization in Additive Manufacturing. Based on Hertz-Mindlin model, Hamaker theory model and Coulomb's law, Van der Waals and electrostatic force are introduced to describe the contact dynamics of nylon powder at preheating temperature. The DEM model of nylon powder at preheating temperature was established based on the mechanical parameters and the rationality of the model was verified by comparing with the experimental results. The flow process of nylon powder in a heated rotating roller was simulated by DEM which checked the correctness of the model. The effects of particle size and particle size distribution on the flow characteristics of nylon powder were studied. The results show that the adhesion force of nylon powder is the result of the interaction of electrostatic force and van der Waals force. With the increase of particle size, the collapse angle of nylon powder decreases and the fluidity of nylon powder increases. And the nylon powder fluidity with uniform particle size distribution is stronger than that of Gaussian particle size distribution. The results can guide the optimization of powder spreading process in SLS.