Li-ion batteries have been widely used. However, the safety concern is always serious due to its high energy density. In order to improve the safety of the batteries, it is necessary to use the protection integration circuit. In this article, the concept for realizing the safety protection of Li-ion batteries during charging and discharging is described briefly. A circuit design using Seiko BMS chip S-8209 is purposed. Based on this, a simulation was performed and verified using Pspice program, which provides a theoretical basis for the circuit design.