Rainfall gauges (meters) are the main observation instrument of precipitation. In order to ensure the accuracy of the measurement results, the calibration and field verification are very necessary. A rain gauge (meter) indoor test instrument is devised, which can also carry out calibration in outdoor tests. The calibrating instrument uses the measurement standards traceable to the ball as the standard. A peristaltic pump is used for the constant velocity control of rainfall intensity and a power controller and a storage battery are used to realize the outdoor rainfall instrument calibration without the alternating current. Through the analysis of tests and application, it is found that its performance is better than similar domestic products, and it complies with the measurement standards of traceability for rain gauges (meters). It is applicable to calibration and field verfication, and can be used for the field verification of rainfall sensors in automatic weather stations.