Pyrite is one kind of metal sulfide minerals distributed very widely and in non_uniform form in nature. Once the environmental conditions are changed, pyrite is very prone to be oxidized. Furthermore, human activities would accelerate oxidation of pyrite, reduce the strength of rocks, and trigger a lot of engineering geological problems. If the metal ions such as calcium are present in the geological environment, it is very easy for them to combine with sulfate and form gypsum. When the sulfur in pyrite generates the same moles of gypsum, the mineral volume would increase by more than 5 times in this process, and this would cause damage to the construction project due to non-uniform distribution. Pyrite oxidation and decomposition form water-soluble minerals such as jarosite with the continuous reaction. These weathering minerals are dissolved and often form small cavities, resulting in the formation and transformation of the underground fluid and increasing damages to projects. Despite the fact that the damage of pyrite weathering to projects has aroused some attention, further studies are needed to investigate and interpret geological problems caused by weathering of pyrite on the basis of geochemical theories.