The use of Additive Manufacturing (AM) is increasing at a fast rate in wide ranging industries, aerospace, medical technology, transport and energy. One of the manufacturing methods used in this field is based on powder processing, but its major bottleneck is associated with the quality of particle spread layer in the powder spreading process, as its underlying particle dynamics remains unknown, which is sensitive to the type of spreader and the cohesive interaction between particles. Here, the particle dynamics in the powder spreading process for a gas-atomised metal powder was explored by discrete element method (DEM), using the most realistic physical and mechanical properties of the particles. The velocity and trajectories of particle within the heap, and the quality of the particle spread layer, were compared in the blade and roller spreading processes. Their sensitivity to the cohesive interaction between particles were also explored. The results showed that compared to blade spreading, there were several velocity bands in cascading style and particle convection within the heap in the roller spreading process, due to the rotational motion of the roller spreader. Before the formation of particle spread layer in roller spreading, the particles needed to climb upward and slip downward along the edges of heap, resulting in longer trajectories of particles. With the increase of particle surface energy, the total particle volume of spread layer was reduced in both blade and roller spreading. Compared to blade spreading, the total particle volume of spread layer in the roller spreading was smaller and more sensitive to particle surface energy. This could be attributed to the formation mechanisms of particle spread layer, i.e. the ability of particles within the heap entering into the gap region between the rough base and spreader, and the drag effect of particles by the spreader in the gap region.