The water level sensor was mainly used for water level measurement in underground water tanks, pipelines and other places of coal mines. The digital water level sensor designed in this paper was based on the constant current source driving method to achieve water level acquisition. The sensor used Cortex-M3 processor, built-in 24-bit ADC acquisition, and the internal reference voltage accuracy was high, which was affected by environmental temperature drift small. The electrical signal output by the water level sensing element was used for signal acquisition through the ADC differential end of the processor, data analysis and processing, calculation of the water level value, and the basic error of the test within the full-scale range was far less than the standard specification of ± 0.2 meters. Experimental results showed that the sensor had the characteristics of high accuracy, stability and reliability, and anti-interference ability, which was suitable for monitoring the water level in mining.