This paper introduces the structure configuration and realization method of upper monitoring system of a medium and small substation and mainly completes selection and control of communication settings and real-time refreshing and display of field data collected, etc. Due to the requirement for real time performance of monitoring system, how to ensure stable serial communication has become the core problem of the whole software, and meanwhile considering that a lot of real-time data needs to be collected and a mass of historical data needs to be kept in power system, and therefore local database is also an important component of this monitoring system.