Abstract: According to the actual measurement and control requirements of water level of hydraulic accumulator in the energy-saving and water- saving frequency conversion irrigation system, software and hardware of a intellectual water level monitor with high accuracy for measuring and controlling water level were developed based on MCS-51 single chip computer. Some technical shortcomings of common digital liquid level meters, such as the complex calibrating process, the temperature drift of the preset values, and the single and imperfect controlling mode were overcome in this monitor. Some application shortcomings of other digital intellectual meters, such as the requirement of high standard input signal, the complex parameter setting process were abolished in this monitor. The results of the performance test and practical application showed that the system had the stable performance and the convenient operation, as well as the high ratio of performance to cost, so that it was successfully applied in the water saving irrigation.