Abstract: In order to improve the design of programs to reduce casing wear in oil and gas wells, an experimental study was conducted to evaluate mechanisms that relate to casing wear.Under simulated downhole conditions, the drillpipe-casing friction wear tester was used to identify how contact forces influence casing wear by changing test loads.Then, S45C, S55C, N80 and P110 casings were tested in drilling fluids with different densities, so as to compare their wear resistance with different weighting agents.It was found that the casings were seriously worn in non-weighted drilling fluids, but with the increase of drilling fluid density, the casing wear rate decreased quickly and then increased gradually.The weighting agent led to the most effective wear reduction when the mass ratio of barite and iron ore powder was 2:1.The results showed that there is an approximate linear relation between casing wear rate and contact force.When the contact force is controlled in a certain range, the casing wear can be minimized by reasonably choosing weighting agent and casing materials.The casing wear efficiency relates to the ratio of tensile strength to yield strength in power function.The empirical formula of casing wear efficiency was given in the paper, it can provide a reference for predicting the casing wear.