The invention discloses an adaptive impedance protection method for a parallel capacitor. According to the method, the voltage and the current of the capacitor are monitored; automatic calibration ofcapacitor initial impedance of the capacitor in operation is carried out; real-time impedance of the capacitor in operation is calculated, true impedance of the capacitor is updated dynamically and periodically, the real-time impedance is compared with the true impedance, if a relative value of a modulus of real-time impedance change amount does not exceed the dynamic update limit threshold and the update period is reached, the true impedance is updated, if the relative value exceeds the dynamic update limit threshold, update failure alarm is emitted; if the relative value exceeds the set protection alarm threshold and time delay reaches, fault alarm is emitted; if the relative value exceeds the set protection tripping threshold and time delay reaches, a tripping exit is protected. The method is advantaged in that the method is suitable for various fault conditions of capacitors and capacitor sets, setting values are simple to calculate, the method is simple and convenient for realization, and protection sensitivity and reliability of the capacitor are effectively improved.