The elastohydrodynamic lubrication model of gear rack transmission is established,considering the gear that is modified and thermal effect,comprehensively considering the variation of equivalent radius of curvature,entrainment velocity and the alternating load along the line of action and the gear tooth modification,the numerical solution of unsteady-state elastohydrodynamic lubrication of the gear rack with time-dependent loads is analyzed. The influence of modified coefficient on the oil film pressure and film thickness of the gear rack is studied and the influence of positive modification and negative modification on central film thickness and minimum film thickness are also analyzed. The results show that the positive modification could reduce the oil film pressure and increase the film thickness which could improve the lubrication of the gear rack,negative modification causes the oil film pressure rises and the film thickness become thinner. Therefore,in order to in accordance with the requirements of the premise when designing the gear rack mechanism,the positive modification gear should be selected to avoid the negative modification gear.