The invention discloses a method for producing sodium dichromate through cationic membrane electrolysis. The method comprises the following steps: mixing a 20-40% industrial sodium chromate solution and a 23-50% sodium dichromate solution to obtain a mixed feed liquid with a volume ratio of sodium dichromate to chromate being equal to (1.5:1)-(5:1); introducing the mixed feed liquid into an anode chamber and introducing a sodium hydroxide solution with mass concentration of 27-30% into a cathode chamber; switching on direct currents, wherein the current density is controlled to be 2-4kA/m<2>, the electrolysis temperature is 70-90 DEG C, the pressure difference between the cathode chamber and the anode chamber is 200-500mmH2O, the anode feed temperature is 50-85 DEG C, and the cathode feed temperature is 55-90 DEG C; and after electrolysis, obtaining sodium dichromate and oxygen gas in the anode chamber, and obtaining sodium hydroxide and hydrogen gas in the cathode chamber.