In order to solve the poor accuracy and low stability problems of the real-time measurement system of paddy rice moisture content in combine harvester, a real-time sampling platform for paddy rice was set up, based on which the real-time measurement system of paddy rice moisture content in combine harvester was designed by capacitance method. The hardware circuit of the detection system was designed and the monitor interface of the master computer was developed to realize the communication between the master computer and the slave computer. The master computer can display and store monitoring information in real time. The influence of temperature and impurity rate on capacitance difference was analyzed and the performance of the sampling platform was verified. The relation models of capacitance difference, temperature and paddy rice moisture content output were established. The coefficient of determination was 0.9866, and the model was verified. The results showed that the impurity ratio of paddy rice was less than 1.2% after sieving by sampling platform. The maximum error of the detection system in laboratory testing was 0.42%, the average error was 0.22%, the average relative error of the detection device was no more than 1.25%. In the field validation test, the relative error of the detection device was less than 3%, which effectively improved the accuracy of on-line detection. The research result can provide a reference for on-line access of paddy rice moisture content.