The temperature field of heavy rail during cooling in walking beam cooling bed has been studied using ANSYS thermal analysis and continuously measuring the actual temperature. The theoretical prediction values of the surface temperature of heavy rail, the straightening temperature and corresponding cooling time are in reasonable agreement with experimental results. The simulation shows that the maximal temperature difference in cross section of heavy rail is 9112 ℃, and the temperature distribution is uniform when heavy rail reaches straightening temperature, and the temperature difference is not exceeded by 5 ℃, and the maximal temperature difference in cross section of heavy rail increases with the increase of heat transfer coefficient. The temperature distribution in cross section can be more uniform by reducing the cooling velocity before coming to the maximal temperature difference, and the capacity of walking beam cooling bed can be changed through adding fans.