gear trains are the critical components in a railway traction system as they transmit andrnwithstand very high loads. Their primary function is to transmit power from one shaft to thernother. In the railway traction system, there are several arrangements for the drives system. Inrnthis particular case the unit that takes power, from motor assembled to drives system throughrnpinion on the shaft to the final spur or wheels by means of single stage or compound stage onrnthe axle of the train, in such a way that power is transmitted. During the transmission ofrnpower from one shaft to another, for rail vehicles moving in high speed, torque is alsorntransmitted. In this phenomenon, different kinds of stresses and deformations will occur onrnthe structure of the gear train. FEM (Finite Element Method) is used to determine and analyzerndifferent kinds of stresses and deformations in the complex geometry. This thesis investigatesrnthe characteristics of gear trains under different kinds of loading, including bending and shearrnstresses, stresses due to vibration, contact stresses and deformations by FEM and proposes arnbetter optimization for the gear units. rnTwo or three spur gear trains with and without idler gears are modeled in both solid worksrnand ANSYS work bench for drives system to distinguish the behaviors of the stresses andrnvibration for the system, and optimization will be proposed for the design of the gears. Thenrnthe result obtained will be compared with the analytical method. Contact stresses are alsornanalyzed and compared with the current method which is known as Hertzian contact stress; ifrnboth value agree very well, FEM is then the accurate method to analyze the effect of therncontact stress for the gear units in the drives system. American Gear ManufacturesrnAssociation (AGMA) is used for stress analysis but it is limited and many assumptions to berntaken into account. Lewis equation is also used to determine the bending stress. Afterrndifferent kinds of analysis, the parameters which may affect the overall efficiency of thernsystem will be optimized, by proper treatment and design of the gear structure for the drivesrnsystem. These treatments will also include improving tribological property of the gears,rnprofile modification of the gear tooth and so on. Therefore, FEM will predict the differentrnkinds of stresses and deformations on the gear train structures of electric traction train .