People now emphasize on the research and development of agricultural greenhouse due to its key position in protected agriculture. The objective of this article is to research and test the thermodynamic function of the heating pipe of water heating system in greenhouses. The content of the article is: to do some theoretical analysis and calculation of the thermodynamic function of the heating pipe of water heating system; to perform some practical tests of the thermodynamic function of the heating pipe from the sealed-chamber Lab. Through theoretical analysis and practical test, the formula of the coefficient of heat-transfer of the heating pipe was obtained, and the reliability and the influential factors of the formula were analyzed.