As an industrial by-product, phosphogypsum has become a promising candidate for reducing environmental pollution and improving resource utilization efficiency. However, the mechanical properties and durability of phosphogypsum-based materials are limited, necessitating modification to enhance their overall performance. To improve the performance of phosphogypsum-based composite concrete ( PGC) , nanosilica ( NS) was incorporated into the mixture to produce NS-modified PGC ( PGC-NS) . The results indicate that PGC-NS with 1. 5% NS content ( PGC-1. 5NS) exhibits excellent performance, achieving a 28-day compressive strength of 63. 8 MPa and a softening coefficient of 0. 98. Fourier transform infrared spectroscopy and thermogravimetric analysis reveal that the incorporation of NS promotes the hydration reaction of PGC-NS, leading to the formation of more C-S-H gel. Sustainability analysis shows that the energy consumption and carbon emissions of PGC-1. 5NS are only 34% and 28% of those of C50 concrete, respectively, highlighting its significant environmental and low-carbon benefits. The research findings provide new insights for the modification of phosphogypsum-based composite concrete and offer guidance for promoting the green development of concrete.