Abstract: In order to improve the rolled quality of pipe stretch-reducing process, reduce energy consumption, exactly control finishing temperature, and thus offer scientific set values to pipe tapping temperature, based on analyzing the mechanism of heat transfer, a mathematical model of heat transfer in pipe stretch-reducing process is derived, in which the boundary conditions in the processes of descaling, rolling and air cooling are provided. The equation of deformation heat in rolling deformation zone is also obtained using the variation principle of plastic material. The results indicate that the effect of deformation heat on the steel pipe's thermal distribution should not be ignored. The mathematical model provided can present the pipe's temperature fluctuation and agree well with the testing values in the process of stretch-reducing. Accordingly, the model can be used in the parameter analysis and technologic optimization of the processes of steel pipe reheating and stretch-reducing.