Pluviometer is an important instrument for meteorological,hydrographic and agricultural departments to measure rainfall.Newly produced or in-service pluviometers are all need to be checked to guarantee the precision and reliability.Yet the manual checking method is not convenient and the checking soutits precision is hard to guarantee.For this reason,we designed a portable automatic calibrator for pluviometer.It uses ultrasonic to detect the liquid level and then controls the stepper motor to regulate velocity and flow automatically,thus keep the water flow evenly.Different rainfall can be set via the software to simulate the real rainfall.The measurement precision is calculated by comparison of the pluviometer readings with the software set values.To ensure the checking precision,we use high-frequency ultrasonic transducer and the timing frequency of CPU reaches 50 MHz.Experiment results show that the calibrator has high checking precision,and can preferably meet the requirements of the existing meteorological observation.