In order to improve the unit efficiency, a small hydropower plant in Guizhou finally realizes the optimal active power control allocation and establishes a unit efficiency on-line monitoring system by using multi-channel ultrasonic flow measurement technology. This paper focuses on the system function and program design and implementation methods and so on. After the system was installed and debugged in a small power plant in Guizhou, all the functions were tested, and did efficiency test at the same time. This system can use a variety of methods to achieve efficiency curve fitting, and can be compared, the overall has a certain degree of innovation.