Abstract: In the paper, according to the actural operating condition and management level of many distribution substations,the microcomputer monitoring device based on a single chip processor was studied. And its hardware and software structures were discussed. The device can not only be used to measure alternating voltage, current, power factor, active power and inactive power, but also provide many functions, such as power load and power factor control, voltage quality statistics, lost-phase protection, and printing out. One year s application showed that the device presents good performance and high reliability.