The aerodynamic drag resistance is the main constraint on the performance of high speedrnrolling stock technology. Its effect increases as speed of train increases and with poorrnaerodynamic body shape design of high speed train body. Problems such as passengerrndiscomfort, safety conditions reduction, environment disturbance, and more traction powerrnconsumptions are main effects of aerodynamic drag resistance. This thesis investigates therneffect of aerodynamic drag resistance of passenger rolling stock of two high speed train modelsrnwith leading car, middle coach, and tail car. The first train model is existing European ICE-2rnRegional Train and the second modified train model is called Ehio-HST-250+. Thernaerodynamic investigation is done using CATIA V5R20 modeling software and ANSYSFluentrnrnV 17.0 Computational Fluid Dynamics (CFD) simulation software. The numericalrnmethod used on Fluent solver is viscous-incompressible steady state Reynolds Average NavierStockrn(RANS)rnandrntwo equationrnturbulencernmodelrnofrnRealizablernkrn-rnεrnmodelrn(RKΕ)rnwithrnNonequilibriumrnwallrnfunctionrn(NWF)rnofrnnearrnwallrntreatmentrnforrnthernsimulationrnofrnthernsystemrninrnanrnrnopenrnairrncondition.rnTherninputrndatarntornthernCFDrnsoftwarernarerncollectedrnfromrnrelevantrnliteraturesrnrnwithrnrnconsideration of Ethiopian average air temperature of 25°C for input air propertyrnvariables. The study does not include passenger discomfort, safety conditions (cross wind,rntunnel test etc.), pantograph component, and vibration of the vehicle as time and computingrnmaterial quality limits. Thus using steady RANS CFD method in open air condition, reductionrnof coefficient of aerodynamic drag percentage amount of 49.01% of enormous aerodynamicrndrag is reduced and 636.13 kW traction power is saved. This can increase the safe and comfortrnenvironment of the system.