The invention discloses a process for removing sodium oxalate from a sodium aluminate solution through lime causticization. The process comprises the following steps of: (1) adding a fine aluminum hydroxide crystal seed cleansing solution into part of red mud wash water, adding a lime additive into a diluted cleansing solution (sodium aluminate solution) containing sodium oxalate according to a molecular ratio of CaO to Na2C2O4 of 0.6-2.0, and reacting for 10-90 minutes at 30-70 DEG C under an enhanced mass transfer condition; (2) performing solid-liquid separation on slurry after reaction to obtain the sodium aluminate solution without the sodium oxalate and an underflow containing calcium oxalate; and (3) adding the sodium aluminate solution without the sodium oxalate into a last tank for red mud washing or a penultimate washing tank for red mud washing, and adding the underflow into the last tank for red mud washing or discharging the underflow along with red mud. According to the process, the sodium oxalate in the sodium aluminate solution can be economically and efficiently removed through lime causticization, the lime addition can be significantly reduced, the causticization rate of the sodium oxalate is improved, the reverse causticization of the calcium oxalate is effectively inhibited, and the alkali consumption is reduced.