An adaptive protection method for impedance of parallel capacitors comprises monitoring a terminal voltage and current of the capacitor; automatically calibrating the initial impedance of the capacitor when the capacitor is put into operation; calculating a real-time impedance of the capacitor during operation, dynamically updating the actual impedance of the capacitor periodically; comparing the real-time impedance of the capacitor with the actual impedance, updating the actual impedance if the relative value of the modulus of the real-time impedance change does not exceed the dynamic update limit threshold and the dynamic update reaches update period; generating an update failure alarm if the relative value of the modulus of the real-time impedance change exceeds the dynamic update limit threshold; generating a protection alarm if the relative value of the modulus of the real-time impedance change satisfies the protection alarm condition and the delay time is reached; and protecting the trip outlet if the relative value of the modulus of the real-time impedance change satisfies the protection trip condition and the delay time is reached. The protection method is applicable to various fault conditions of the capacitor and the capacitor bank, the set value is simple to calculate, the implementation is simple, and the sensitivity and reliability of the protection for capacitor are effectively improved.