Abstract: Predicting the variation of thermal history during laser additive manufacturing of metallic materials can effectively improve the forming quality and ensure the high dimensional accuracy of formed parts. A three-dimensional transient mathematical model that can predict the temperature field of laser directed energy deposition（LDED） with time and space online was established by using the finite difference method with grid activation and boundary adjustment. The temperature at the center of the melt pool and the temperatures at different places behind the center of the melt pool were predicted. Finally, the temperature calculated by the model is verified by deposition experiments, and the simulation time is only 83.5% of the actual processing time.