In the calibration process of the double tipping bucket rain sensor, for the rain gauge with different rain intensities in the opposite direction, it is necessary to adjust the positioning screw of the upper tipping bucket and the capacity adjustment screw of the metering tipping bucket respectively. At the same time, it is also necessary to record the turnover times of the upper tipping bucket and the metering tipping bucket. The rain gauge uses a passive pulse output. Each time the measuring bucket is flipped, it triggers the reed tube to produce a pulse. The signal can be collected by the single-chip microcomputer and recorded automatically. However, the turning times of the up-tipping bucket depend on manual observation and statistics. Because the tipping speed of the up-tipping bucket is fast, the manual counting is inaccurate, resulting in an inaccurate calibration. In addition, only one rain gauge can be manually recorded at a time, which cannot automatically record data in batches. In this paper, the optical fibre sensor is used to automatically count the number of tipping buckets under the condition of the rain gauge’s non-contact and non-interference operation to provide accurate calibration data.