It's difficult to form hydrodynamic lubrication because of the low viscosity of water, but it is founded by experiment that there is low co-friction on water lubricated plastic alloy bearings working. The main factors that affect co friction are revs, loaded and clearance. Significance and effect of every factor that affect co friction is analyzed by variance analysis and orthogonal experiment. goaphs of every factor that affect co friction are list. From the goaphs, it is founded that there is elastic hydrodynamic because of elastic deformation in the plastic alloy.