Abstract: In order to timely acquire the situation of entrainment losses of the tangential-longitudinal-axial combine harvester when it harvest in a field, an tangential-longitudinal-axial threshing-separating test bed was built in the laboratory, which was made up of a knife-type teeth tangential-axial drum, assistant feeding wheel and spike teeth longitudinal-axial drum of the tangential-longitudinal-axial combine harvester. The threshing-separating performance test was conducted with the test bed at the wheat feeding rate of 7 kg/s, the components and the distribution regularity of the threshed mixture were measured, the threshing-separating coefficient matrix was established and then threshing-separating matrix equation of threshing-separating device on the tangential-longitudinal-axial combine harvester was solved. The array PVDF (Polyvinylidene Fluoride) piezoelectric-film sensor was applied to measure the grain number of the 11th materials boxes location under spike-tooth longitudinal-axial drum of the tangential-longitudinal-axial combine harvester, the measured results were compared with the entrainment losses which was calculated by the threshing -separating matrix equation. The result showed that the their difference between the measured entrainment losses in the field and calculated values was -4.82%- -5.87%.It has real-time monitor for grain entrainment losses in the field.