The invention discloses a power grid impedance adaptive method for an active power filter. The power grid impedance adaptive method comprises the steps of performing current collection; calculating an instantaneous current value error, comprising a formula which is as shown in the specification; calculating an effective current value error, a formula which is as shown in the specification, wherein i<*>(k) is a set current instantaneous value of the k sampling point of the active power filter; i(k) is an actual current sampling current of the k sampling point of the active power filter; I<*> is a set n-degree harmonic effective value of the active power filter; I is an actually output current effective value of the active power filter; N is the number of sampling points of a power frequency period; performing weighing normalization processing on the effective current value error and the instantaneous current value error to obtain an equation which is as shown in the specification; making comparison between the normalized weighed error en and an error threshold value Er, if the absolute value of en is greater than Er, not performing compensation in the actual operation of the active power filter, and controlling a parameter Pn to be equal to 0; and if the absolute value of en is less than or equal to Er, performing correction on the control coefficient Pn of the active power filter: comprising a formula which is as shown in the specification.