Abstract: The linear thermal expansion coefficient of materials is very important in the fields of precision instruments and high precision experiments.To measure the linear thermal expansion coefficient of some ultra low expansion(ULE)materials,the laser interferometer is usually used.In our experiments,the two interferential arms of the laser interferometer are fixed on one bracket,whose the purpose is to compensate the optical path changes caused by other effect except the elongation of the materials.Using this interferometer,not only the linear thermal expansion of the bracket can be counteracted,but also the ground vibration can be counteracted effectively.We measure the linear thermal expansion coefficient of the materials at the level of 10-6/℃ by this laser interferometer.If the technique of the experiment is improved on and interferential stripes are stabilized,this kind of interferometer can used to measure the linear thermal expansion coefficient at higher level.