Objective To explore the coronal alignment of tibial prosthesis after osteotomy using personalized extramedullary positioning technique on tibia side in total knee arthroplasty (TKA). Methods A clinical data of 170 patients (210 knees) who underwent primary TKA between January 2020 and June 2021 and met the selection criteria was retrospectively analyzed. Personalized and traditional extramedullary positioning techniques were used in 93 cases (114 knees, personalized positioning group) and 77 cases (96 knees, traditional positioning group), respectively. The personalized extramedullary positioning was based on the anatomical characteristics of the tibia, a personalized positioning point was selected as the proximal extramedullary positioning point on the articular surface of the tibial plateau. There was no significant difference between the two groups in gender, age, body mass index, surgical side, course of osteoarthritis, and Kellgren-Lawrence classification (P>0.05). The preoperative tibial bowing angle (TBA) formed by the proximal and distal tibial coronal anatomical axes in the personalized positioning group was measured and the tibia axis was classified, and the distribution of personalized positioning point was analyzed. The pre- and post-operative hip-knee-ankle angle (HKA), the lateral distal tibial angle (LDTA), and the postoperative tibia component angle (TCA), the excellent rate of tibial prosthesis alignment in coronal position were compared between the two groups. Results In the personalized positioning group, 58 knees (50.88%) were straight tibia, 35 knees (30.70%) were medial bowing tibia, and 21 knees (18.42%) were lateral bowing tibia. The most positioning points located on the highest point of the lateral intercondylar spine (62.07%) in the straight tibia group, while in the medial bowing tibia and lateral bowing tibia groups, most positioning points located in the area between the medial and lateral intercondylar spines (51.43%) and the lateral slope of the lateral intercondylar spine (57.14%), respectively. The difference in HKA between pre- and post-operation in the two groups was significant (P<0.05); while the difference in LDTA was not significant (P>0.05). There was no significant difference in preoperative LDTA and HKA and the difference between pre- and post-operation between groups (P>0.05). But there was significant difference in postoperative TCA between groups (P<0.05). The postoperative tibial plateau prosthesis in the traditional positioning group was more prone to varus than the personalized positioning group. The excellent rates of tibial prosthesis alignment in coronal position were 96.5% (110/114) and 87.5% (84/96) in personalized positioning group and traditional positioning group, respectively, showing a significant difference between groups (χ2=7.652, P=0.006). Conclusion It is feasible to use personalized extramedullary positioning technique for coronal osteotomy on the tibia side in TKA. Compared with the traditional extramedullary positioning technique, the personalized extramedullary positioning technique has a higher excellent rate of tibial prosthesis alignment in coronal position.