A new type of capacitive grain moisture on-line measuring device was designed based on the measuring principle of non-contact parallel plate floating capacitor, which was suitable to continuous dryer under severe environment. The static batching measurement was used to improve the repeated accuracy of the measurement. Positioned filling device was designed to eliminate the measuring error caused by the variation of porosity and different way of filling. Wireless communication technology was adopted to achieve real-time data transmission from client sensors to computer and overcome the poor drying conditions, which could affect data transmission. The relationship among moisture, temperature, and capacitance of corn was calibrated and the system was tested on a continuous dryer. The results showed that the correlation coefficient between results of oven method and results of online measuring system was 0.992, and the absolute error of measurement was less than ±0.4%, while the working temperature was 15~50℃, relative humidity was 80%~100%, drying temperature was 70℃, and the corn moisture content range was 14%~21%. It proved that the online measuring system meet the design requirement of poor drying conditions.