Abstract: The temperature and humidity controller consists of MCS51 singleboard computer, A/D convector,output circuit,　display circuit, alarm circuit, temperature and humidity sensor， etcs. The controllable range of the instrument is temperature （－40～11℃）±0.5　℃， relative humidity（0～100％）±（2％～3％）. The controller has run in a cold storage plant since 1991． Test results show that the controller has the feature of high control precision and can lower down the fluctuation of temperature and humidity in cold storage plant, thus resulting in improved quality of cold storage products and less power consumption(reducing 8 ％～10％ in average).