Abstract: A kind of monitoring system for combined harvesters cleaning losses was designed. The symmetry sensors were used to eliminate machine vibration interferences. The stimulating signals were processed by charge amplifier bandpass and antialiasing filter, and the signals of cleaning losses were then extracted effectively. The single-chip computer unit was used for monitoring and counting in real-time. The results of laboratory test and field test showed that the designed monitoring system can effectively monitor combined harvesters cleaning losses, and the maximum measurement error is 2.81%, which meets the practical monitoring requirements.