A grain moisture detection system is proposed in this paper, which is designed based on capacitive sensor and single chip microcomputer. The working principle of concentric capacitive sensor is introduced and the hardware circuits of system are described in details. The system has an intelligent controller internal, it can collect data, display data and determine whether to alarm when the data overreach threshold. The system is tested in practice and the measuring errors are analyzed, experiment results showed that the system has high measuring accuracy and good controlling capacity; it can meet the needs of moisture measuring.