In view of the current railway industry's demand for fuel consumption control of diesel locomotives and improvement of fuel consumption management level, a locomotive oil quantity monitoring system based on NB-IoT is designed and implemented. The system uses high-precision ultrasonic liquid level sensor to obtain the liquid level of the oil, uses GPS to obtain the latitude and longitude in real time, uploads it to the server through the NB-IoT communication module, and stores it in the database after filtering algorithm, and thus monitors the real-time by oil quantity data, view historical oil quantity and fueling record using the browser access management system, realizes remote management of equipment. The test results show that the design can monitor the oil quantity, the precision is high, and the control of fuel consumption is improved. It has certain reference significance for the research of NB-IoT application and monitoring system.