Abstract: The high and low temperature region spatial anomalies of thermal image exists approaching rock failure under loading. In order to make quantitative study on the variation of aggregation degree of high temperature point, the infrared experiment was carried out in the condition of uniaxial compression, with the high temperature point being extracted according to the ninety-fifth percentile of the infrared temperature field and analyzed through the method of quadrat analysis. Using the diffusion coefficient to quantitatively measure the aggregation degree of high temperature points, the variation characteristics of the spatial distribution of high temperature points in the loading process of siltstone was studied. The results show that: in the process of loading, the fluctuation of the diffusion coefficient is weak, the increasing trend obvious and the stage characteristic is fast-slow-fast change like reverse "S"; in the stage of plastic deformation and post peak, rapid rise characteristics of diffusion coefficient of infrared high temperature points can be used as a precursory anomalies of rock steady loss, whose occurrence probability can be up to 80 %.