Additive manufacturing (AM) is a prevailing topic. Among all the processes during AM, the initiation and evolution of melt pool is of vital importance. Lots of studies are devoted to the fundamental mechanism of melt pool, but most of them only focus on the macroscopic level. However, when it comes to the mesoscopic level, it can be founded that the melt pool is the result of melting and fusion of powders. To better understand the melt pool, it is necessary to understand the melting and fusion characteristics of powders. This paper aims to provide a new kind of mesoscopic perspective to the melt pool through the investigation on single powder melting. Enthalpy based Lattice Boltzmann method, combined with Neumann boundary, is adopted to model the powder melting under fixed and moving laser beam. Results indicate that for the fixed laser beam, the melting front presents a symmetric convex. The increase of the laser power input can increase the energy absorbed by the powder, speed up the melting process and enhance the flow inside the powder. For the moving laser beam, the melting front loses its symmetry. The increase of the scanning speed can decrease the energy absorbed by the powder, the melting volume fraction and the inside flow. The fast moving speed could easily result in partially melted powder. All these results could help us better understand the powder melting under different laser inputs, and thus arranging the laser power reasonably to make the best use of it according to various occasions.