The lubrication state of open pinion and rack under conditions of low-speed,heavy-load and frequent changing of directions was researched on the rack performance assessment test device of the Three Gorges Ship Lift.The pressure-viscosity coefficient in the calculation model of oil film thickness in open pinion and rack was modified for high-viscosity lubricating oil.The lubrication state of open pinion and rack was analyzed according to the criterion of oil film thickness.The results show that the lubrication state of open pinion and rack under low-speed and heavy-load conditions can be relatively accurate judged by using the criterion of oil film thickness.Speed and load have a great influence on lubrication state,the lubrication condition gets bad and tooth face is easy to be worn or welded while the motion directions of pinion and rack are changing.Thereby,the load and the roughness of tooth surface should be reduced and lubricating oil viscosity should be increased to improve the lubrication state.