During the operation of small current grounding system, unbalanced voltages would be induced in neutral points as the unbalanced parameters of transmission lines. And this unbalanced voltage produces an unbalanced current in feeder system. Therefore, studying the distribution characteristics of the unbalanced current is helpful for analyzing system faults. This article theoretically analyzed the unbalanced current in feeder systems. Starting from the feeder, the equivalent circuit of the system is obtained based on Thevenin's theorem while the expressions for unbalanced currents in feeders are also obtained. Then, under the condition of the singlephase disconnection fault, the influence of unbalanced currents on the amplitude and phase of zero sequence current on feeder lines is revealed. Finally, the simulation model is built in MATLAB to verify the analytical results.