The invention discloses a monitoring system of the battery state applied to an online storage battery pack. The system comprises a data acquisition module, an excitation generation module, a synchronous acquisition signal line, a synchronous channel enabling line, an excitation line and a measuring line, the data acquisition module comprises a switching unit, an isolation unit, a voltage processing unit, an acquisition unit, a single-chip microcomputer, a communication unit, an isolation power supply and an internal resistance processing unit, and the excitation generation module comprises anisolation power supply, an excitation unit, a single-chip microcomputer, an isolation unit and a switching unit. According to the system, synchronous switching of excitation and acquisition is realized through linkage control of the data acquisition module and the excitation generation module, battery information of storage batteries is acquired in real time to monitor the storage batteries in real time, the state of each storage battery is understood, a high-current discharging test of the storage batteries is avoided, the workload is reduced, the work efficiency is improved, the wiring is simple, and the cost is effectively reduced through reuse of devices.