Abstract: In order to explore the infrared anomaly in the process of fracture instability, The fractal theory is introduced to calculate the characteristic roughness of the infrared thermal image of siltstone by the box dimension method.Combining variance and AIRT to analyze the characteristics of the evolution of the characteristics of the sandstone under uniaxial compression.The results show that the evolution of the characteristic roughness of the thermal image is similar to the variance, and it can be divided into three stages.In the compaction stage, The characteristic roughness and the variance increase rapidly, and the variance is well characterized at this stage.In the elastic stage, the characteristic roughness starts to become smaller, and the ability to portray the same as the two.In the post peak stage, the characteristic roughness value is enhanced, and the amplitude and frequency are increased obviously., and in the peak stress, characteristic roughness began to become big, which is infrared precursor information.In this stage, the ability to describe the characteristic is more ideal than variance.