The invention discloses a chlorate removal method in production of a chlor-alkali ionic membrane. Reaction temperature of dilute brine in production of the chlor-alkali ionic membrane is adjusted to 50-55 DEG C through a heater, and then the dilute brine enters a neutral reaction labyrinth trough. A sodium pyrosulfite saturated solution is prepared in a sodium pyrosulfite preparation trough and is added into the neutral reaction labyrinth trough by a delivery pump through a flowmeter to be mixed with the dilute brine 5-10 minutes, and then sodium hydroxide is added. The PH value of reaction liquid is adjusted and controlled to be 10-11 automatically through a PH online monitor, and the treated dilute brine is conveyed to a dissolved salt trench. According to the chlorate removal method, sodium pyrosulfite is added into the dilute brine in the production method of the chlor-alkali ionic membrane, and the chlorate removal rate reaches 96.3% by controlling the reaction temperature, the PH value, the adding quantity of the sodium pyrosulfite and the sodium hydroxide, and the adding time of the sodium hydroxide. In addition, the removel cost is low, and the requirement for clean production is met.