We developed heat deformation analysis model based on that of steel bar using Gaussian distribution in order to quantitatively understand deformation behavior of gas pressure welding of rail. The validity of the developed analysis model was confirmed by the variation of temperature, transition of upset length and geometry of budge through gas pressure welding test of rail. Therefore, it was confirmed that this model could simulate that with high accuracy. We found that the deformation degree at the center of the rail base and the jaw part of the rail head are smaller than that of other parts from results of heat deformation analysis. It is estimated that the deformation degree depends on the shape of rail. This paper describes the developed heating deformation analysis model of gas pressure welding of rail, and its validation test results.