The invention provides an absorption liquid cyclic utilization method and system in a flue gas denitrification process. The method comprises the steps of firstly, utilizing a nitric acid solution as an oxidizing agent to oxidize flue gas, and mixing the oxidized flue gas with alkali liquor to conduct a denitrification reaction; recycling denitrification reaction liquid into a diaphragm electrolytic cell, performing electrolysis to produce nitric acid and alkali liquor, and utilizing nitric acid and the alkali liquor again as the oxidizing agent and the alkali liquor. The system comprises an absorption tower, an alkali liquor storage tank, a nitric acid storage tank and the diaphragm electrolytic cell, and the interior of the absorption tower is separated into a lower-section oxidizing chamber and an upper-section alkali liquor absorption chamber; the nitric acid storage tank is communicated with the oxidizing chamber, and the alkali liquor storage tank is communicated with the alkali liquor absorption chamber; a nitric acid reflux inlet of the absorption tower is communicated with the nitric acid storage tank; a reaction liquid reflux inlet of the absorption tower is communicated with an anode region of the electrolytic cell; the anode region of the electrolytic cell is communicated with the nitric acid storage tank, and a cathode region of the electrolytic cell is communicated with the alkali liquor storage tank. According to the absorption liquid cyclic utilization method and system in the flue gas denitrification process, the removal rate over 90% of oxynitride is achieved, the denitrification reaction liquid is cyclically utilized, no waste water is discharged, and the method and system are safe and environmentally friendly.