In order to improve the accuracy of liquid flow measurement of the open channel,therefore, more accurate flow measurement equipment is needed for industrial and mining enterprises. Based on the analysis of the principle of open channel flow, the design scheme based on DSP28335 is proposed. The flow measurement method of open channel weir is described. The main control chip DSP28335 sends ranging commands to dls-a15 using RS232C serial communication, DLS-A15 receives the ranging command and sends a laser signal to the liquid Surface to be tested. The laser signal reflected back from the liquid level is received by the sensor and converted into a sequence of data information code. It is then returned to the main control chip DSP28335 to receive by RS232C serial communication. The correct data received is the distance from the laser ranging sensor to the liquid level. Experiments show that the device has the characteristics of high measurement accuracy, reliable operation and low price, and provides a reference for online automatic detection of liquid level in the industrial field. The experiment shows that the device has the characteristics of accurate measurement, reliable operation and low price, which provides a reference for online automatic detection of sewage discharge in industrial and mining enterprises.