Abstract: The one dimensional tests were carried on the ballasts with diameters of 6～8 cm,4～6 cm and 2～4 cm in the plexiglass cylinder of 15 cm in diameter and 59 cm in height under periodical fluctuation of boundary temperature to investigate the variation of temperature in the ballasts. Results show that the temperature changes of ballast are unsymmetrical with time and the temperature attenuation is slow with depth and the mean temperature of ballasts is always lower than that on the surface under condition of open system. It implies that there exist two mechanisms of conduction and convection for heat exchanging in ballasts. Inversely, there are no such variation of temperature under condition of closed system. It means heat conduction may be the only mechanism in the test specimen of the designed sizes.