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Alloy steel gear is an important basic part in automatic transmission(AT)and its fatigue life is critical to the AT per- formance. In order to improve the contact fatigue life of gears, the surface conversion coating technology has been introduced into the ap- plication of gear resistance to fatigue pitting. Therefore, the principle of chemical conversion film was employed to generate the soft man- ganese phosphate conversion coatings with several microns on the surface of gears. The tribological performance of coatings was analyzed and evaluated by SRV multifunctional friction and wear tester. The surface characteristics of the coatings were analyzed by a confocal laser scanning microscope(CLSM).The power circulation-type gear test machine and automatic transmission fatigue test bench were used for contact fatigue characteristics of the gears coated with manganese phosphate coating. The fatigue pitting effect of two kinds of automatic transmission fluid(ATF)on gears was analyzed, and the pitting resistance mechanism of manganese phosphate conversion coatings was investigated. The results showed that the initial running compatibility of the gear paired with manganese phosphate conversion coatings was significantly enhanced. A micron-scaled soft layer was generated on the gear surface filled with the most concave-convex cutting rip- ple of the gear surface, which reduced the local maximum meshing contact stress and the friction factor of the metal surface. The oil film and lubrication condition of gear meshing were enhanced by the coating with irregular pits. Surface manganese phosphate conversion coat- ing and a lower friction coefficient ATF might be an effective method to improve the fatigue property of the AT gears.