The control of evolution of flow and heat transfer in melt pool is a key concern and hot topic to improve the produce quality, e.g. fissure and roughness, during the additive manufacture process. Researchers focus on controlling the evolution of melt pool by changing energy balance in melt pool. However, the momentum drive is seldom presented in literatures but fully necessary to further improve the control efficiency. Therefore, a promising magnetic force source is introduced to investigate the controlling effect on melt pool evolution. Based on a developed and validated laser melt pool model, the evolution results of three different magnetic field arrangements and intensities are obtained and analysed compared with that without magnetic force. In addition, the surface shrink characteristics during quenching process are studied to further evaluate the benefit of the added source. Results show that the melt pool evolution is significantly affected by the additional magnetic force. The increasing downward y-component force promotes the transport in melt pool which makes the surface deformation larger, as well as the melt pool dimension. Inversely, with the increase of x-component force, both the surface deformation and the melt pool dimension gradually decrease due to the induced transport limitation. During quenching process, the surface roughness is continuously reduced with a certain increase of the magnetic intensity caused by the increased melt pool duration and slightly vigorous surface flow. However, the improvement effectiveness becomes bad as the magnetic force exceeds a critical value owing to the increased shrink instability. (C) 2018 Elsevier Ltd. All rights reserved.