The coeflieient of linear expansion is one of the important the rmophysieal properties of materials. which is widely used in engineering structure design, machinery manufacturing and other fields. Traditional measurement methods have problems such as low accuracy and great influence by external conditions. In orderto improve the reliability of the measurement data, a new instrument was designed to measure the linear expansion coelficient of an object using two methods at the same time. ln this experiment, the linear expansion of aluminum rods within a certain temperature range was measured by split-tip interferometry and single-slidifl raction ,and the data were processed by matlab, The experimental results show that the two methods can beearried out at the same time without interfering with each other, and the data obtained are relatively accurate, and the new instrument has the advantages of high measurement accuracy , good repeatability and convenicn operation , which provides an effective method for the study of thermal properties of materials.