Slipper pair is one of the most important frictional pairs in piston pump, the oil film lubrication characteristics among them restricts piston pumps lifetime. The passive oil film lubrication theory was researched with a certain type of piston pump as an example. The oil film thickness under different conditions of the pump was obtained. Combined with the lubrication characteristics of nonmetallic materials, the lubrication characteristics of slipper pair were obtained through combining with passive oil film lubrication theory. Nonmetallic material slipper and the passive oil film Lubrication theory can be used to other piston pump according to the theoretical analysis and actual application condition.