In order to solve the problem of process selection for underground on-site deep treatment and reuse of complex mine water with high hardness, high mineralization and iron and manganese exceeding the standard, this study proposed the treatment process consisting of “aeration oxidation + flocculation and sedimentation + multi-media filtration + manganese sand filtration + reverse osmosis”, which had a short process chain, good treatment effect, and stable effluent water quality. Through the pilot test to verify the treatment effect of the optimization and adjustment process, the system consistently produced water with turbidity below 0.5 NTU, iron and manganese below 0.1 mg/L, residual chlorine below 0.1 mg/L, and conductivity below 60 μS/cm, meeting the water quality requirements for underground production equipment. The reverse osmosis recovery rate stabilized at 50%. The study provided valuable guidance for the process selection in the design of on-site treatment and reuse systems for complex mine water with high hardness and high mineralization in underground arrangement.