An aluminum electrolytic capacitor is made by using an aluminum cylinder as the negative electrode, filling it with a liquid electrolyte, and inserting a bent aluminum strip as the positive electrode. It also needs to be treated with a direct current voltage to form an oxide film on the positive electrode plate as the dielectric. Its characteristics are large capacitance, but large leakage current, poor stability, and positive and negative polarities. It is suitable for use in power supply filtering or low-frequency circuits. When using it, do not connect the positive and negative electrodes in reverse.