During the acidification of 160 ℃ high temperature sandstone reservoirs in offshore WC oilfield，the clay minerals such as illite are hydrated and decomposed in hydrochloric acid，causing particle migration and reservoir damage，resulting in reduced productivity of oil and gas wells. To solve the problems of fast reaction at high temperatures，sensitivity of illite clay，and short penetration distance of conventional mud acid，experiments such as high-temperature acid dissolution，core flooding，and produced liquid ions analysis were carried out，and a high-temperature resistant chelating acid，composed of 5% GLDA+8% acetic acid+1%HF+1.5% clay stabilizer NW-1+1% corrosion inhibitor CT-1，was proposed. The chelating acid achieved a dissolution rate of 15.2% at the temperature of 160 ℃ for 16 hours，a corrosion rate of 3.7451 g/（m²·h），and an anti-swelling rate of 90.9% . After the chelating acid interacted with the rock core，Si⁴⁺，Ca²⁺，Mg²⁺，and Fe³⁺ content gradually increased，indicating that the chelating acid had a multivalent metal ion chelating effect，which could avoid secondary and tertiary damage to the rock core by the acid solution，achieving the effect of the acid dissolution on deep penetration of the formation. In response to the lack of mature professional software for chelating acid acidification design，a simplified acid rock reaction plane radial flow model was used， considering the material balance of hydrofluoric acid，a chelating acid acidification simulation design software was developed using MATLAB language. The optimal acid injection rate for Well A was calculated to be 2 m³/min，and the volume of acid used in each section did not exceed 70 m³. The chelating acid system was successfully used to remove blockages in 5 offshore water injection wells. After the measures，the average daily injection volume increased by more than 110 m³，and the injection pressure decreased significantly，with a maximum pressure drop of 12 MPa. The chelating acid system had a good effect on removing blockages and increasing injection in the 160 ℃high illite sandstone gas reservoir.