The thermo-mechanical behavior of the deposited part by a directed energy deposition (DED) process is greatly dependent on the design of the substrate. The thermal-mechanical behavior significantly affects the quality and the reliability of the fabricated part by the DED process. The aims of the paper is to investigate thermo-mechanical characteristics of the design of the substrate on thermo-mechanical characteristics of G6 deposited part on SCM440 substrate by a DED process using three-dimensional transient and non-linear finite element analysis (FEA). From the results of the FEAs, the effects of the substrate design, including the width, the length and the thickness of the substrate, on heat transfer, deformation and residual stress characteristics of the deposited part were examined. Based on the results of the examination, the methodology to choose a proper design of the substrate was discussed. In addition, an appropriate design of the substrate was proposed from viewpoints of thermal characteristics, deformation behaviors and residual stress distributions.