Abstract: The problems such as corrosion of steel rail and the buried metal pipe,and electric shock,interference to communication systems caused by stray current have become prominent increasingly.Through establishing unilateral power supply model of electric locomotive,the paper deducted the mathematical formula for stray current under reasonable suppositions,simulated the formula by using the simulation software Matlab.The simulation result showed that in unilateral power supply range,stray current increased at first and then decreased with increasing the distance to electric locomotive,and it come to maximum at the mid-point of power supply range,the transition resistance and track longitudinal resistivity have great affection to the stray current,the distance and the current of power supply have secondary affection to the stray current.