Objective The contact mechanics and wear performance of mobile- and fixed-bearing UKAs were compared under ISO14243-1:2009 force control standard test condition by computational simulation. Methods The contact stress and Von Mises stress of mobile- and fixed-bearing UKAs under the test condition were analyzed by finite element analyses. Then, the linear wear depth and wear volume of both UKA inserts were obtained after simulating 5 million gait cycles using wear prediction model. Results The maximum contact stresses of mobile- and fixed-bearing UKAs before wear were 15.7 MPa and 44.3 MPa respectively, and the maximum Von Mises stresses were 11.94 MPa and 23.33 MPa respectively. With the increase of wear, the maximum contact stress and Von Mises stress of the mobile-bearing UKA decreased first and then became stable, while that of the fixed-bearing UKA remained basically unchanged. The linear wear depth of fixed-bearing UKA was 1.5 times that of mobile-bearing UKA. But the wear volume of mobile-bearing UKA was 5.4 times that of fixed-bearing UKA, and the wear volume of backside surface accounted for 70% of the total wear volume of mobile-bearing UKA. Conclusion Compared with the fixed-bearing UKA, the mobile-bearing UKA had lower contact stress and Von Mises stress, but larger wear volume. The backside wear of mobile-bearing UKA was an important source of increased wear debris.