Interaction of heat exchanger pipe and its fluid was considered, the fluid domain and solid domain was considered as research object. According to the continuity boundary conditions of temperature and heat flux at coupling interface, iterative format of the interface temperature and heat flux was derived, and convergence method was also derived. Based on whole-domain algorithm, distribution of temperature and heat flux at coupling interface and average exit temperature was studied. For solution accuracy and solution efficiency, partition algorithm with boundary coupling was investigated. The results show that the relaxation factor 0.75, and convergence tolerance 0.1 is appropriate. The partition algorithm of coupled heat transfer is a reliable numerical simulation method for the research and development of efficient heat exchanger pipe.