Abstract: Objective For the additive remanufacturing of 30CrMo parts with volume defects, this study is to clarify the influence of prefabricated groove size on residual stress in remanufactured parts, and to provide a basis for the designing of prefabricated groove size and the controlling of residual stress. Methods Based on the thermal elastoplastic theory and finite element method, and considering the nonlinear variation of material thermodynamic performance parameters with temperature, a thermal mechanical coupling finite element model of the remanufacturing of 30CrMo plate is established by using the simufact welding software. The model is verified to check the correctness and effectiveness of the modeling process. Using the model established, the temperature field and residual stress distribution of the remanufactured parts is analyzed and influence law of the length and width L_c and width W_c of the prefabricated groove on the peak residual stress and the peak residual stress on the path is investigated. Results The residual stress is dominated by length direction of prefabricated groove, followed by width direction of prefabricated groove. And, the high residual tensile stress in length direction of prefabricated groove occurs at the end of the last weld and the base metal near it, while the high residual tensile stress in the width direction of prefabricated groove is distributed in the middle of the first weld and base metal adjacent the first weld. Thus, to avoid high residual tensile stress, the length L_c of the prefabricated groove shall not be less than 10W, where W is the width of a single weld bead. Moreover, the width W_c of the prefabricated groove shall not be greater than 12W. Conclusion The principle for designing of the prefabricated groove size is that the length shall not be too short and the width shall not be too wide. The outcomes provide a reference for the design of prefabricated groove and the regulation of residual stress in the remanufacturing of 30CrMo parts.