In order to solve the condensation problems between thegrain around the heat pipe ingrain warehouse with heat pipe by natural cold source，an electromagnetic valve was added in the heat pipegroup to control operation of the refrigerant in the heat pipe according to the temperature difference between the external environment and thegrain layer around the heat pipe. The micro measuring device of temperature and humidity in warehouse was designed and manufactured. The change of the air relative humidity and dew point temperature difference in porosity of grain bulk was studied； the relationship between temperature control of electromagnetic valve and condensation was discovered.The results showed that in the range of 5℃～20℃， the higher thegrain moisture content， the higher the dew point temperature of the air in the barn， the smaller the dew point temperature difference. In natural cold source low temperature heat pipegroup， the calculation formula for the temperature control of the electromagnetic valve was:y=-0.2149x3+7.439x2-86.384x+343.43(the y was the temperature control of the electromagnetic valve； x was the moisture content of wheat). This research provides the theoretical foundation and technical support for the practical application of heat pipe technology in largegrainwarehouses.