Fertilizer application is an important part of rice production， which affects rice yield and may cause environmental pollution， therefore， it is important to study the technology of precision variable fertilizer application.The monitoring system for the discharge of a hinged lever type fertilizer box， which can actively monitor the remaining fertilizer quantity of fertilizer box in real time， was designed on the self-designed rice direct seeding synchronous side depth fertilizer application machine to realize the real-time monitoring of the accuracy of fertilizer application.The monitoring system consists of a weighing device and a multiplexed fertilizer discharge monitoring device.The weighing device consists of hinged lever frame， balance beam load cell， etc.The parallel beam load cell is used as the working element to carry the fertilizer box installed above the hinged lever mechanism and the real-time fertilizer gravity inside the fertilizer box.The multi-circuit fertilizer discharge monitoring part consists of the controller， fertilizer discharge monitoring， data communication， monitor， etc.It collects the fertilizer discharge signals obtained from each load cell and transmits them to the monitor interactive interface after processing， so that the operator can easily view and configure the operational parameters of the fertilizer application system in real time.The results of the field trial showed that the maximum relative error of monitoring was 4.79% and the minimum was 3.55%.The monitoring system is combined with the fertilizer discharge volume monitoring system based on the rotation of the fertilizer discharge shaft， which can realize the real-time self-adjustment of the fertilizer discharge volume of the fertilizer applicator.It will provide reference for the research of intelligent fertilization technology and equipment.