In order to test the performance of grain loss monitoring sensor and search for the best installed location, a calibration test-bench which composed of lifting platform, lifting driving mechanism, feeding device and the sensor installation platform was designed. Full wheat grain, blighted wheat grain and stalks with different lengths were selected as calibration materials to test the performance of grain loss monitoring sensors in different installation heights and installation angles. The laboratory tests showed that for different moisture wheat samples, the measurement error of grain loss monitoring sensor could be limited to less than 4.8%. The installed location of the grain loss monitoring sensor was determined when monitoring the separate loss according to laboratory calibration results. The field tests showed that the average separate loss monitoring error was 3.40%.