The invention relates to a method for deep purifying of boron-containing radioactive waste liquid and recovery of boric acid. The method comprises the following steps of performing filtering, heat exchange, high-pressure reverse osmosis and low-pressure reverse osmosis on the boron-containing radioactive waste liquid to form a concentrated liquid and a permeate liquid, and directly sending the permeate liquid into a monitoring discharging tank to discharge; evaporating and boiling the concentrated liquid under the vacuum condition, performing mist and foam separating, condensing and cooling on secondary steam generated by the steam to form a condensed liquid, sending the condensed liquid into the monitoring discharging tank to discharge, and sending the remained concentrated boron liquid after evaporating to perform the boric acid crystallizing and recovery treatment; cooling and crystallizing the concentrated boron liquid generated by the concentration of the boric acid, so as to obtain a crystal slurry containing boric acid crystals; separating the solid and liquid of the crystal slurry to obtain a boric acid solid product; capturing radioactive nuclides in a clarified mother liquid after solid and liquid separating of the crystal slurry by an ion exchange column, returning back to perform the boric acid concentration, and then concentrating. The method has the advantages that while the boric acid is recovered, the waste liquid can be deeply purified; the size of equipment is greatly reduced, the treatment energy consumption is greatly decreased, and the discharging of secondary waste liquid to the outside is avoided.