Abstract: To improve the measurement reliability of the seed rate on wheet planter, a capacitance seed rate sensor was developed according to the principle of capacitance variation of medium mass. The signal condition circuit as designed with AD7745 convert and a single chip microcomputer, and short line connection betweent the sensor and conditon circuit was used to decrease the stray capacitance of the sensor. The founction relationship between the sensor capacitance and seed rate was obtained according to the calibration. The results showed that the maximum error of the sensor was 2.2% in different seeding rate. The sensor can test the seed rate well on line and provide strong support for variable seeding.