Focusing on the two major problems of industrial solid waste accumulation and heavy metal contaminated soil, to explore the solidification effect and internal mechanism of a low-carbon curing agent used for treating 1% copper-contaminated soil. The changes in leaching concentration of copper ions and heavy metal forms in solidified soil were compared and analyzed. Meanwhile, the changes in the mechanical properties and microstructure of solidified soil were detected. The data indicates that the copper ion concentration of solidified soil after soaking complies with environmental safety requirements, and heavy metals transitioned from carbonate-bound state to iron-manganese oxidized state. The proportion of exchangeable and residual states in solidified soil do not change significantly, but their contents are different. In addition, soaking has a significant effect on improving the early strength of solidified soil and promoting the early hydration reaction. Microscopic results indicate that water curing promotes the formation of significant cementitious and needle-like substances in the solidified soil. The Fourier transform infrared spectrometer (FTIR) results show that the presence of O—H, C${O}_{3}^{2-}$, and Si—O/Al—O groups in the solidified soil. Comprehensive analysis shows the presence of conventional hydration products such as calcium carbonate and hydrated calcium silicate in the solidified soil, as well as the formation of ettringite under the action of phosphogypsum. As a result, the pores in the soil are effectively filled, and heavy metal ions are well encapsulated and adsorbed in the product, resulting in a leaching concentration of heavy metals that meet the requirements, while also promoting the strength of the solidified soil. The reasearch results provide a new approach for industrial solid waste, as well as a low-carbon and effective solidifier for the treatment of copper-contaminated soil, which has important environmental, economic, and social benefits.