Objective: To analyze the preoperative influencing factors of varus after Oxford unicompartmental knee arthroplasty. Methods: A total of 660 patients (767 knees) undergoing Oxford unicompartmental knee arthroplasty in adult joint reconstruction surgery department of Beijing Jishuitan Hospital from January 2018 to December 2019 were retrospectively analyzed. Inclusive criteria: diagnosis was osteoarthritis, single compartment lesions in the medial side of the knee; preoperative flexion deformity was less than 10°, active range of motion was greater than 90°; preoperative X-ray full-length images of both lower limbs showed less than 15° varus (Noyes method); anterior cruciate ligament was well functioned, The cartilage of lateral compartment of knee joint was intact. Exclusion criteria: combined with other inflammatory arthropathy; combined with extraarticular deformity; previous knee surgery history. The average age of the patients was (64.4±8.1) years, including 153 males and 497 females. The degree of post-operative varus was measured with Noyes method. The total patients were divided into varus group (Noyes≥3 °) and normal group (Noyes<3 °). Gender, age, body mass index (BMI), range of motion (ROM), preoperative flexion deformity (FD), American Knee Society pain score (AKS) and American Knee Society function score (AKS function) were recorded. The standard anteroposterior and lateral X-ray films of knee joint and full-length lower extremity kinematic line films were taken by Sonialvision Safine Ⅱ (Shimadzu, Japan) multi-function digital tomography system. The image was measured by picture archiving and communication system (PACS). The following angles were measured preoperative Noyes angle, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA) and joint line converge angle (JLCA) were measured and analyzed. Results: Gender(P=0.346), operative side (P=0.619), age (P=0.746), BMI (P=0.142), preoperative ROM (P=0.102), preoperative knee pain score (P=0.131) and functional score (P=0.098) were not risk factors for postoperative varus. The influencing factors of postoperative varus were preoperative MPTA<84 ° (P= 0.018, OR= 3.712, 95%CI: 1.250-11.027), preoperative Noyes > 5°(P=0.000, OR= 3.105, 95%CI: 1.835-5.254), preoperative FD > 5° (P= 0.001, OR=1.976, 95%CI: 1.326-3.234). Pre-operative LDFA (P=0.146) and preoperative JLCA (P= 0.709) had no significant effect on postoperative kinematic line. Conclusion: Patients with severe preoperative varus, especially those with varus deformity mainly from the tibial side, and those with preoperative flexion deformity are more prone to get varus lower extremity kinematic line after Oxford unicompartmental knee arthroplasty.