A harmonic protection method for a capacitor bank uses a harmonic protection apparatus, which includes a CPU unit, a current and voltage sampling unit, and a protection device. The CPU unit obtains effective value I1 of fundamental wave current of the capacitor bank, and effective value In of the n-th harmonic wave current of the capacitor bank, where n is harmonic order and ranges from 2 to ∞, and calculates the true effective value I of current of the capacitor bank by I = I 1 2 + ∑ n = 2 ∞  k n  I n 2 provided that kn=rn/r1, kn is the n-th harmonic coefficient , rn is power consumption equivalent resistance of the capacitor bank for the n-th harmonic, r1 is power consumption equivalent resistance of the capacitor bank at a fundamental frequency. When I≧1.3 IN, the CPU unit controls the protecting device to disconnect the capacitor bank, provided that IN is a threshold current of the capacitor bank.