The invention provides a method for improving reliability of a compressed air system. The method comprises the steps that an air supply system use for a first air storage tank, a second air storage tank, a third air storage tank and a fourth air storage tank is reformed, a mother tube drain pipeline and a blowdown valve are installed and led in a drain well, one of outlet pipelines of the first air storage tank, the third air storage tank and the fourth air storage tank is led out, connected to the interior of a mother tube, then led out from the mother tube, and connected with an original outlet pipeline, the original outlet pipeline of the second air storage tank is not changed, a pipeline is led out from the mother tube and connected with a reserved valve, a second air storage tank connecting opening is reserved in the mother tube and connected with the second air storage tank, a fifth original 10m3 air storage tank and a seventh original 10m3 air storage tank are removed, and two vertical air storage tanks are reinstalled, all cast iron valves are replaced with stainless steel valves, and an air storage tank blowdown secondary door is installed additionally. The method for improving the reliability of the compressed air system effectively ensures safe and stable operation of the compressed air system and units of the compressed air system, avoids occurrence of major accident of unit shutdown, and effectively reduces the power consumption rate of a plant.