To address the issues of inadequate sharing accuracy, irrational current distribution, unbounded droop coefficient values, and slow state of charge (SOC) balancing in traditional droop control, this paper proposes a novel SOC balancing droop control method based on an improved droop coefficient. First, the shortcomings of traditional power index form droop control are analyzed, and a new droop coefficient form embedding a nested arctangent function into the power index is proposed to limit the droop coefficient values, thereby enhancing system stability and reliability. Subsequently, to tackle the problem of slow SOC balancing speed, an acceleration factor Q is introduced into the droop coefficient to improve the balancing speed, and the impact of different Q values on the droop curve is analyzed. Finally, a simulation model is constructed to validate the proposed method through comparative analysis. Simulation results demonstrate that the improved method significantly accelerates SOC balancing when the SOC difference is small. During the balancing process, the droop coefficient varies more smoothly, and the bus voltage does not exhibit significant oscillations even when the SOC difference is large.