Abstract: Low-pH (pH<11) cementitious material is the key to the construction of high-level radioactive waste (HLW) disposal repository. In China, the first underground research laboratory (URL) for gelogical disposal of HLW is located in Xinchang site of Beishan area, Gansu province, and the construction work was started in June of 2021. In order to support the construction of Beishan URL and future disposal repositories of the HLW, the crushing-leaching method was adopted to study the change rule of the pH values of the ordinary Portland cement (OPC) with different mineral admixtures, such as silica fume (SF), fly ash (FA), ground granulated blast furnace slag (GGBFS), and the low-pH cementitious material was prepared in this paper. To satisfy the goals of various types of water in HLW repository should be lower than 11, reliability of low- pH cementitious material was validated by penetration, soaking, and extreme leaching methods. For understanding the engineering properties of low-pH cementitious material, its hydration products, compressive strength, rheological parameters were analyzed by using XRD, SEM and combined with other indoor laboratory tests. Finally, hardened sample of low-pH cementitious material was soaked in Beishan groundwater, and its influence on groundwater environment was assessed by studying the change process of main ion concentration in soaked water. The results show that the pH values of the hardened samples are linearly correlated with the weight ratios of CaO/SiO₂ containing in the cementitious material, and the low pH base ratio is the mixture of the OPC with 40% SF, and if compunding admixtures of SF and FA were added in OPC to reduce the cost of lowpH cementitious material, the weight ratio of CaO/SiO₂ should be lower than 0.53. pH values of penetration and soaking water in the hardened mixtures of OPC with 40% SF are below 11 after about 28 days and 90 days, respectively, and the maximum values is about 11.2 if the hardened samples decompose to loose particles on a 10 000-year scale, which are satisfied with the requirements of repository. Comparing with OPC, due to pozzolanic reaction and micro-aggregate effect of SF, the 150-day hydration product of low-pH cementitious material dose not content Ca(OH)₂, and the compacted CSH gel leading higher the 28-day compressive strength of the mortar, but the viscosity of grouting slurry is higher under the same water/cement ratio. When hardened sample of low-pH cementitious material is soaked in Beishan groundwater with the water-solid ratio of 1∶1, concentration of main ion such as Na⁺, K⁺, Ca²⁺, Cl^- and SO^2-₄ in the soaked water are almost invariable after 90 days, and has smaller influence on the groundwater environment.