Converters usually use droop control in DC microgrid, but excessive droop coefficient will lead to system instability in droop control. Stability research is a key issue of DC microgrid. This paper establishes the small signal modeling of DC microgrid considering line impedances and local loads, and focuses on the influence of system parameters on system stability. Therefore, the range of parameters are obtained when the system is stable through poles distribution. This paper designs reasonable system parameters to achieve SOC equalization. Finally, simulation verifies the correctness of the above theoretical analysis.