Objective: To investigate the effect of single Osteochondral Defect (OCD) of the knee on the pressure distribution in the weight-bearing area of the medial femoral condyle, and to further evaluate the changes of the location of peak pressure on the medial condyle with the size of the defect. Methods: 10 fresh porcine knee joints were fixed in extension position. First, mechanical loads were applied to the medial compartment of the normal pig knee joint to determine the maximum contact pressure area. Then, osteochondral defects of different diameter in depth of 9 mm were drilled at this area, respectively. Axial compression loads of 100.0 N, 200.0 N, and 300.0 N were applied to the medial compartment of each knee joint, and the strength and location of the peak contact pressure during loading were recorded. Results: The peak pressure increased with increasing defect size, and showing stress concentration. The peak pressure was significantly higher in the defect diameter ≥8.0 mm than in the non-defect knee (When 300.0 N pressure was applied, 8.0 mm defect VS. no defect, 1.526 ± 0.1218 MPa VS. 1.330 ± 0.0793 MPa, P = 0.0113). In addition, the peak pressure showed a similar tendency to move closer to the defect rim as the defect size increased (the distance between the peak pressure position and the defect rim (peak-to-rim distance): when 300.0 N pressure was applied, 8.0 mm defect VS. 4.0 mm defect, 3.178 ± 0.1373 mm VS. 3.903 ± 0.1545 mm, P < 0.0001). Conclusions: In the single knee osteochondral defect model, when the diameter of the defect at the bear-loading zone was ≥8.0 mm, the peak pressure on the uninjured site significantly increased, and peak-to-rim distance significantly decreased, which implied 8.0 mm as a potential threshold for surgical intervention.