Abstract: In power system, harmonic detection is the basis of the analysis and control of power quality, e.g., reactive power compensation and harmonic filtration. In order to overcome the shortcoming of the traditional methods, this paper proposes a harmonic detection method by combining Gerschgorin disk criterion and Toeplitz approximation method (TAM). This method is based on the models of signal spaces. Gerschgorin disk criterion is employed to detect the source number. Besides, both the orthogonality of signal subspace and noise subspace and the rotational invariance of subspaces are combined to estimate the signal frequency. And then, the signal amplitude is obtained by utilizing total least squares(TLS) algorithm. Finally, it is shown from simulation experiments and real data analysis that the proposed algorithm can attain higher speediness and better precision.