Due to the widespread use of the channel is in an opening shape, and the water level in the channel height is a changing value, which brings great difficulties to open channel flow measurement of water. This paper introduces a kind of intelligent open channel flow device with velocity of self calibration, according to the water level value, automatically adjust the height velocity sensor in the water and correct the the average velocity in two sections of open channel, it realizes the accurate measuring of water level, instantaneous flow and cumulative flow in open channel.