Abstract: In order to study the mechanical properties of the pyrite slag in the Northern Guizhou area after replacing the concrete aggregate, the X-ray diffraction instrument was used to analyze the phase and mineral composition of the pyrite tailings slag in the Northern Guizhou area. Pyrite tailings slag will be used to prepare pyrite tailings slag modified concrete. Its mechanical properties and freeze-thaw characteristics will be studied. The results show that the increase of the pyrite tailings slag content can prolong the setting time of the improved concrete. When the pyrite tailings slag content is 20% and the water-cement ratio of concrete is 0.40, the 7 d compressive strength and 28 d compressive strength of the modified concrete are the highest. Under the same hydration time, the hydration heat release rate, hydration heat release and DTA value of concrete continue to decrease with the increase of the pyrite tailings slag content. At the same time, as the number of freeze-thaw cycles continues to increase, the compressive strength of concrete continues to decrease and the frost resistance index also continues to decrease. This shows that freeze-thaw cycles can weaken the ability of cement-solidified soil to resist deformation and reduce the bearing capacity.