Abstract: The experimental study of heat transfer and flow resistance characteristics of single phase water in three flat tubes with different structural dimensions was conducted. At the same time, suitable criteria were selected to evaluate the heat transfer enhancement efficiency of flat tubes within the experimental scope and the optimal working region was determined. The results indicate that flat tubes can greatly enhance the single-phase turbulent flow heat transfer and the maximum heat transfer coefficient attains to 2.62 times of that in smooth round tube. The maximum quantity of heat transferred from flat tubes attains to 2.2 times of that in smooth round tube with the same heat exchange area and pump power.