This study focuses on two major issues: industrial solid waste accumulation and heavy metal contaminated soil, aiming to explore the solidification effect and underlying mechanism of low-carbon solidifier applied to treat 1% copper-contaminated soil. The article compared and analyzed the changes in leaching concentration of copper ions and heavy metal forms in solidified soil, and detected the changes in mechanical properties and microstructure of solidified soil. The data shows that the copper ion concentration of solidified soil after soaking meets environmental safety requirements, and heavy metals transition from carbonate bound state to iron manganese oxidation state. The proportion of exchangeable and residual states in solidified soil has not changed 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 FTIR results indicate the presence of O-H, CO32-, 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 were effectively filled, and heavy metal ions were well encapsulated and adsorbed in the product, resulting in a leaching concentration of heavy metals that met the requirements, while also promoting the strength of the solidified soil. This article provides 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.