Abstract: The measurement of linear expansion coefficient of silicon was performed in high temperature with the high accuracy laser interferometric dilatometer developed by China National Institute of Metrology. The single frequency laser interferometer and symmetrical beam path are adopted in the dilatometer. The resolution of the interferometer is within 1nm. In order to make the measurement in the temperature of over 800 K, the furnace of this system was redesigned and the experiment method was modified. With the renovated system, the linear expansion coefficients of silicon were measured by stepwise heating in the temperature range of 800K～1200K. The changing process of specimens and the results of the measurement were analyzed. The linear expansion coefficient of silicon as a function of temperature was obtained. The measurement in nanometer level for the linear expansion coefficients of material was realized by laser interferometric method in 1200K.