There are two faults in the operation of electromagnetic flowmeter: One is the fault of the instrument itself, i. e. the failure caused by the damage of the instrument structure or components, and the other is the malfunction caused by external causes, such as improper operation distortion, deposition and scaling. This paper probes into these two kinds of faults. Three, the flow measurement is not inconsistent with the actual value of 1. Reason Analysis (1) The Transmitter circuit board is intact; (2) when the liquid velocity is too low, the liquid contains tiny bubbles, and the bubble rises above the pipe gradually, the fluid flow of smooth flow area changes, gas will also generate interference signals, affecting the accuracy of measurement; (3) Signal cable is not connected to the phenomenon or the use of the process of cable insulation loss caused by incorrect measurement; (4) The parameter setting value of the converter is incorrect. 2. Solution (1) Check the transmitter circuit board is intact. If the junction box water or erosion is measured by the liquid erosion, can lead to the electrical function decreased or damaged. The circuit board should be replaced at this time. (2) Ensure that the flow of the liquid in the pipeline is measured at the lowest flow threshold, so that the transmitter can work properly. (3) Check the signal cable connection and the cable insulation function is intact, if the signal cable loosening phenomenon, the connection can be again; if the insulation of the cable does not conform to the insulation requirements, a new cable is required. (4) To reset the converter set value, and the converter's zero point, the full value of the calibration. Fourth, the output signal is full of measure 1. Cause analysis of this kind of failure is roughly: (1) The signal cable wiring is wrong or the cable connection is disconnected; (2) The converter's parameter setting is inaccurate; (3) converter and sensor model do not match. 2. Solution (1) Check that the signal circuit is connected properly or not, if the signal circuit is disconnected, the output signal will exceed the value of the full degree, at this time need to reconnect the signal cable accurately.