A coplanar electrode capacitance online moisture sensor was developed, which has higher precision, more compact configuration and easier installation compared w ith traditional parallel electrodes and cylindrical moisture sensors. An active shield electrode was invented to block the outside electric field, thus the stra y capacitance was decreased and the precision and sensitivity of the sensor was increased according to finite element analysis. A comparative circuit was used t o avoid the influence of shield electrode on drive electrode. Experiments were c onducted on grains with 6%～36% moisture content on a custombuilt equipment. Th e relationships between sensor output frequency and grain moisture content were investigated for each temperature condition and the result was compiled into sof tware to realize temperature compensation which decreased the error from 5% to 1 %. Experimental validation proved that the sensor had a small measuring error of 1％ and was applicable to moisture content range of 6%～36% and temperature ran ge of -10～80℃. 