The thermal expansion property of NICALON Sic multifilaments reinforced Al preformed wire has been measured in the range of 15-400℃. The thermal expansion processes are made two times for one sample and the expansion curves of the first and second time are different. The averaged thermal expansion coefficients are respectively 3.2×10^-6℃^-1 and 4.1×10^-6℃^-1 for the first and second thermal cxpansion processes. The thermal expansion performance has been analysed theoretically and the calculated values are approximately in agreement with the experimental data.