In this article, a two-dimensional model of earth thermal fields was established by using the law of energy conservation and equation of heat conduction to study the annual dynamic heat transfer characteristics of heat exchangers in underground Energy Reserving Systems (UERSs). This model consists of the identification of original soil temperature, and the solutions to the heat transfer equations of single pipes, U-bent pipes and multiple pipes and the equation of variance of earth thermal fields in the transitional seasons. Demonstration tests and simulated tests in shanghai, China, proved this model had a high degree of accuracy in calculating the distribution of earth thermal fields, the amount of exchanging heat at the depth per unit of circuit, the precision parameter of heat transfer, the EWT and LWT in the buried pipes and the area of heat exchangers. A first set of heating and cooling supply systems of underground energy reserving with 10 KW was constructed, which has been running and testing Continuously for three years. A great deal of reliable data was obtained for the testing on the theory model and lots of final suggestions were provided. The above achievements will throw the light on applying and promoting the UERSs in China. The research is also a project sponsored by the China National Natural Science Fund and the article is a summary of this project.