Previous third body studies for wheel/rail are mainly concentrated on water or oil condition. However, friction modifiers (FMs) represent a new approach to managing adhesion coefficient in wheel/rail interface. In this paper, the position of the FM-air meniscus was given as input parameter, the thickness of FM can be solved easily with the multi-grid method. Non-Newtonian fluid model and micro-EHL analysis combined to obtain the relation between the adhesion coefficient and the quantity of FM. The results show that the quantity of FM has a significant effect on the initial adhesion coefficient within a certain range. Besides, the initial adhesion coefficient decreases gradually until it reach stable value with the increase of the quantity of FM.