Abstract: In view of the orifice structure which was much smaller than the dam, the sub-model method was introduced, and the problem of cut boundary value was solved, and then the method of reducing error of the time and space domain was put forward. Then, the accurate simulation of the orifice structure of concrete dam was achieved. Based on the method and a RCCD project, the simulation of the temperature and stress field was carried out, and the variation and distribution of temperature and stress of a typical orifice structure were analyzed in detail. The results showed that the large tensile stress occured at early age (10-30 d), and the maximum appeared in the first winter. In addition, the sub-model method can provide an effective way for studying the temperature and stress field of dam orifice structure.