Abstract: When using active power filter (APF) for harmonic compensation, the harmonic currents need to be detected accurately in real time, and the detection accuracy will directly affect the harmonic compensation effect, at the same time, in order to realise the flexible compensation of harmonics, the specified harmonic current detection is needed. In this paper, a specified harmonic current detection method is proposed based on the double second-order generalised integrator (DSOGI) and cascaded notch filter (NF), which can simultaneously obtain the positive-sequence and negative-sequence components of the specified harmonic current, and the method has the features of high detection accuracy, strong robustness, strong frequency adaptive capability and easy implementation, etc. Finally, the accuracy of the specified harmonic detection of the method is verified by simulation with a three-phase uncontrolled rectifier load as an example.