A new type of red mud/slag/wastewater-based geopolymeric grouts (RSW) was prepared to solve the problem of wastewater and red mud to environment and promoting the safe construction of geotechnical engineering. The applicability of RSW was investigated using different red mud, alkali activator and wastewater dosage. Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD), semi-calorimetry, Scanning electron microscope-energy dispersive spectrometer (SEM-EDS), and Si Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) were conducted to study the effect of wastewater on RSW. The results showed that wastewater has an accelerating effect on the geopolymerization process of RSW, the mechanical strength increased first and then decreased with the increment of wastewater dosage, the 28 d compressive strength of RSW was 30.2 MPa, which is higher than the cement-based grouts. The leaching of heavy metals were lower than 0.4 mg/L, which demonstrates that the RSW has a good immobilization effect on the heavy metals. The FTIR and SEM-EDS analysis results showed that the ions in wastewater could participated in the geopolymerization process and the hydrated products has a immobilization effect on the heavy metals. Overall, this contribution explores utilizing red mud and wastewater, and preparing high performance grouts for underground engineering.