The invention provides a brine refining process for removing calcium and magnesium by one step, which comprises the following steps of: pumping saturated brine out of a brine tank by using a pump, dividing the saturated brine into two paths for heat exchange to preheat the brine to 45 to 60 DEG C, and causing the preheated brine to enter a reactor; adding NaOH and Na2CO3 into the reactor, wherein the NaOH and the Na2CO3 partially come from chlor-alkali production process wastewater; performing refining reaction to completely remove Mg<2+> and Ca<2+> from the brine to make 0.2 to 0.5 g/L the concentration of the NaOH and 0.3 to 0.5 g/L the concentration of the Na2CO3 in the brine, and causing the brine to automatically flow into an intermediate tank; and pumping the treated brine into an HVMTM membrane filter for filtration, adjusting a pH value to 8.5 to 10.5 by using hydrochloric acids, adding sodium sulfite to completely remove free chlorine, detecting that suspended solid (SS) content is 0.1 to 0.2 mg/l, and causing the brine to automatically flow into a refined brine tank to prepare fresh brine. The calcium and magnesium impurities are removed simultaneously so as to simplify the process; and the use of ferric chlorides is avoided so as to reduce material consumption and the emission of pollutants.