According to the eddy current testing principle of electromagnetic induction characteristics, this paper designs a set of electromagnetic induction water quality monitoring system. According to the electromagnetic induction measuring technical to design system excitationdetection coil measurement model, the system is in the Arduino core processor, using digital frequency synthesis (DDS) to create sinusoidal excitation source and then based on the phase AD8302 chip to design the phase detector. And processing a signal of system (filtering, amplification) to increase system reliability, through the serial port and LCD display to achieve humanmachine interface to show magnetic induction signal detection data. Finally, through testing the different types of water samples, the results show that the magnetic induction water quality monitoring system can measure conductivity differences in the water samples as well as determine the water quality categories.