The invention relates to a process and a device for treating high-hardness and high-alkalinity strong brine from iron and steel plants. The process includes steps of (1), feeding the high-hardness and high-alkalinity strong brine into chemical feeding, hardness removing and reaction devices, separately adding sodium hydroxide into the chemical feeding, hardness removing and reaction devices at two steps, mixing and stirring the high-hardness and high-alkalinity strong brine and the sodium hydroxide and carrying out sufficient reaction; (2), feeding the high-hardness and high-alkalinity strong brine mixed with chemicals into a concentration and sedimentation tank; (3), feeding mixed liquid formed by the high-hardness and high-alkalinity strong brine and sediments in the concentration and sedimentation tank into tube micro-filtration membranes, carrying circulation filtration on the high-hardness and high-alkalinity strong brine and the sediments, feeding hardness-removed produced water into a pH (potential of hydrogen) regulating tank and feeding strong liquor back to the concentration and sedimentation tank; (4), adding hydrochloric acid into strong brine in the pH regulating tank to regulate the pH of the strong brine until the strong brine is neutral, then feeding the strong brine into a reverse osmosis device and concentrating the strong brine; (5), recycling produced water of the reverse osmosis device as new industrial water and delivering concentrated water to the iron and steel plants for carrying out heating stuffing treatment on splashing slag or steel slag. The process and the device have the advantage that the problem of influence on local aquatic ecological environments of enterprises due to the fact that high-hardness and high-alkalinity strong brine only can be treated and discharged at present can be solved.