Based on eigenvalue decomposition（EVD） and fast independent component analysis（FastICA） methods， this paper proposes a new method to detect the harmonic/inter-harmonic in power systems. First， the single-channel power system signals are transformed into multi-channel observation signals with time delay transform without any prior knowledge. By EVD of observation signal auto-relation functions， the number of independent frequency components in original harmonic/inter-harmonic is determined， which is used to correct the dimension of the observed signal matrix. Then， FastICA algorithm is adopted to separate and extract various frequency components， and frequency of each component is estimated by spectrum analysis. Finally， amplitude and phase of each component is accurately detected by least square method. Simulation results prove the feasibility， accuracy and validity of the proposed method.