Abstract: To reveal the distribution characteristics and evolution mechanism of hydration heat temperature field of long-span concrete filled steel tubular (CFST) arch bridge in mountainous area, the full-scale model experiment and transient thermal analysis on hydration heat temperature field of long-span CFST arch rib segment with strong radiation and temperature difference were conducted based on the Yarlung Zangbo River Bridge. The calculation method of hydration heat temperature field was proposed, and the direct theoretical relationship between temperature and solar radiation, wind speed and ambient temperature was established. The results show that:The radial temperature field distributes as a symmetric tri-linear model with an influence depth of D/4 at night, and in the afternoon distributes as an asymmetric tri-linear model with a sudden change at D/8~D3/8 from the sunny side interface. The circumferential temperature field distributes sinusoidally with a half wave ratio of about 5:1. The temperature gradient direction on the sunny side changes continuously with a maximum positive temperature difference of 30℃ and a maximum negative temperature difference of 40℃. Coating low radiation absorptivity materials can effectively reduce the temperature gradient. The temperature field calculation method proposed is not limited by climate environment, and the agreement of the final computation results with the experimental data and finite element data indicates indicates the engineering applicability of this method.