Abstract: The paper put forward a design scheme of on-line monitoring system of VRLA batteriy and introduced hardware and software design of the system.The system can monitor parameters of voltage,current,and temperature of VRLA battery in realtime,so as to know the status of charging and discharging of VRLA battery,estimate the residual capacity,and avoid influencing life of VRLA battery due to over charging and over discharging.The system can discharge to a group of VRLA batteries through the software of upper comuter regularly and it resolves the problem of premature failure of VRLA battery due to long-term floating charging.