Abstract: A four-ball tester is used to evaluate the anti-wear property of lube oil under variable load and speed conditions, and a concept of anti-wear characteristic parameter R is proposed through analyzing parameters (load P and speed V) which cause the mutation of friction coefficient. The characteristic parameter R is related with the product of P×V at the mutation of friction coefficient for testing oil and reference oil, i.e. R is defined as the ratio of testing oil P×V to that of reference oil. Test results show that by introducing parameter R and using R to update PB and PD value, it is helpful to distinguish the difference in antiwear performance of lube oils from the same type.