Automatic drainage control of sump and pond were achieved through discrete component circuit, and a low cost, high practical value water monitor was designed. Super high and low water level treatment based on independent circuit could automatically control electric circuit. Water level of low voltage testing pool changed to signal control relay turn-off to control water pump drainage and complete whole operating circle of water pump drive and park automatically, which could guarantee liquid level in fairly ideal range.This equipment with simple structure, low cost, high sensitivity and energy saving was appropriate for various drainage of pond, sump and rainwater collection pool.