Laser-based manufacturing process such as selective laser melting, sintering, and direct deposition using metallic powders plays an important role in additive manufacturing technology. As spatial resolution increases, there is a great need to advance the design, quantitative analysis, and optimization of relevant thermal fluid processes at the powder level. In this paper, a theoretical model is developed to characterize melting and Marangoni flow dynamics within a pure metal powder heated by a moving Gaussian laser beam. Phase field formulation is developed to simulate the solid-liquid phase transition along with the thermocapillary effect at the free surface, which drives the molten flow within the powder and thus influences heat transfer behaviors. The formulation, simplification, and computational results for two-dimensional cases are demonstrated and discussed in detail. (C) 2017 Elsevier Ltd. All rights reserved.