Tailings is the main filling material for mines, which belongs to the typical loose medium and has obvious compressibility under the action of external force and its gravity. Its physical mechanical properties will change with the compaction conditions, but there is no reasonable calculation method to predict these properties of the tailings so far. The tailings of Dahongshan copper mine are used as an example in this study, where a mathematical relationship between density of the tailings and the load which meets the characteristics of the power function is obtained employing a user-defined function in original software that is fitted with the results of the high pressure consolidation test. The mathematical relationship between density of the tailings filling body of a large goaf and the height which meets characteristics of the power function is derived by analyzing the vertical forces balanced of the unit volume of the tailings, the function is integrable, it can be known form the function, density of the tailings increases with the height, the growth rate decreases gradually. The results of the numerical simulation and the industrial field test show that the compaction model of the tailings filling body under its dead weight is in agreement with the real conditions; so that the model has high practical value in engineering.