Abstract: :In view of problems of bad accuracy and real-time existed in harmonic and inter-harmonic detection algorithm, a harmonic and inter-harmonic detection algorithm based on comb filter and subgroup idea was proposed, and a harmonic monitoring device based on the algorithm was designed. Firstly, the device uses the comb filter to separate harmonic and inter-harmonics from original signal effectively. Then, the device uses inter-harmonic subgroup algorithm to calculate inter-harmonic component of the separated signal, and uses original signal component to minus the inter-harmonic component to reconstruct of sampled sequences. Finally, the device adopts harmonic subgroup algorithm to calculate the harmonic component, so as to realize high precision detection of harmonic. Test results verify that the device has high detection accuracy.