This study aimed to evaluate the outcomes of three-dimensional (3D) Printing-Assisted Osteotomy in treating varus knee deformity from old tibial plateau fractures. The study retrospectively analyzed patients with varus deformity induced by old-tibial plateau fractures between January 2019 and June 2023. All patients utilized 3D printed models for surgical planning. The Lysholm Knee Score (LKS), Visual Analog Scale (VAS) and Knee Society Score (KSS) were measured for functional outcomes. Medial Proximal Tibial Angle (MPTA), Joint Line Convergence Angle (JLCA), Mechanical Axis (%MA), Medial Tibial Plateau Depression (MTPD), and Femorotibial Angle (FTA) were measured for radiological outcomes. 15 patients (12 males and 3 females) were included in this study and followed up for 21.9 ± 8.6 (range, 12 to 28) months. Healing of the osteotomy sites were achieved in all patients at 15.8 ± 1.5 (range, 13 to 18) weeks. The knee varus deformities were significantly corrected as reflected by %MA (2.13 ± 13.1°(range, -20 to 22) versus 57.06 ± 9.8°(range, 41 to 70), p < 0.01), FTA (186.7 ± 3.2°(range, 181 to 193) versus 172.3 ± 2.1°(range, 169 to 175), p < 0.01), JLCA (5.8 ± 1.7°(range, 3 to 8) versus 1.3 ± 0.8°(range, 0 to 3), p < 0.01), and MPTA (5.6 ± 1.2°(range, 3 to 8) versus 1.2 ± 1.1°(range, -1 to 3), p < 0.01). Postoperative knee function showed dramatic improvements as reflected by VAS (4.6 ± 1.6 (range, 1 to 7) versus 0.7 ± 0.9 (range, 0 to 2), p < 0.01), KSS (50.1 ± 16.5 (range, 27 to 88) versus 88.5 ± 5.2 (range, 80 to 95), p < 0.01), and LKS (49.5 ± 10.2 (range, 37 to 69) versus 89.2 ± 2.5 (range, 87 to 94), p < 0.01). 3D printing technology provides a valuable tool for understanding deformities and optimizing osteotomy strategies, thereby improving surgical efficacy and treatment outcomes. Its clinical application is highly recommended.