To achieve sustainability and environmental protection capability of ultra-high-performance cementitious composite (UHPCC), glass sand (GS) was used to replace river sand in UHPCC to produce glass sand ultra-highperformance cementitious composite (GS-UHPCC). The effects of different glass sand substitution rates and particle sizes on the compressive and bending properties of GS-UHPCC were investigated through mechanical property tests, the bending toughness and energy absorption capacity were quantitatively characterized as well. In addition, the Xray diffraction and scanning electron microscopy methods were used to analyze the toughening mechanism of the glass sand. The results show that replacing river sand with glass sand with an average particle size of 0. 27 mm is the most effective at a substitution rate of 40%. After substitution, the compressive strength of GS-UHPCC increased by 17. 0%, and the flexural strength increased by 14. 8% compared to the unaltered mixture after 28 days of curing.The energy absorption capacity was optimal, and the microstructure was dense, and the hydration reaction was almost complete. The optimal glass sand substitution rate and particle size obtained in this study can provide feasible support for the application of GS-UHPCC.