A high stability double-pass laser interferometer that can be used for measuring the length changes of materials is introduced. Since the measurement beam and the reference beam of the interferometer have similar traveling pathes and the optical path difference is mainly caused by the sample itself, the interferometer has has strong resistance to external disturbances such as ambient temperature changes and vibration. The stability of the system is verified by the experiment of measuring the reflection film of a plane mirror, which shows that the standard deviation of the measurement data is 4.2 nm in 6.5 hour. This interferometer can be used for high-accuracy dimensional change measurement such as the measurement of the coefficient of linear thermal expansion of materials.